Students can practice the best Class 9 Science MCQ and Class 9 Science Exploration Chapter 8 MCQ Online Test with Answers Journey Inside the Atom for exam preparation.
Class 9 Science Chapter 8 Journey Inside the Atom MCQ
Journey Inside the Atom MCQ
Class 9 Science Chapter 8 MCQ online test
Question 1.
Which of the following statements correctly reflects the early ideas about the nature of matter proposed by ancient philosophers?
(A) Matter is continuous and cannot be divided further.
(B) Matter is composed of indivisible particles called atoms based on experimental evidence.
(C) Matter is made up of extremely small indivisible particles, proposed as a philosophical idea without experimental proof.
(D) Matter consists only of charged particles arranged in a nucleus and orbits.
Answer:
(C) Matter is made up of extremely small indivisible particles, proposed as a philosophical idea without experimental proof.
Ancient thinkers such as Acharya Kanada, Leucippus, and Democritus proposed that matter is composed of extremely small, indivisible particles (parmanu or atomos).
Question 2.
How is a sub-atomic particle like a proton is different from an electron?
(A) An electron is much heavier than a proton.
(B) An electron carries more charge than a proton.
(C) A proton can be easily removed from the atom, but not an electron.
(D) A proton is positively charged, whereas an electron is negatively charged.
Answer:
(D) A proton is positively charged, whereas an electron is negatively charged.
Electrons and protons are sub atomic particles of atom. Proton is different from electron because proton is positively charged whereas an electron is negatively charged.
Question 3.
Rutherford’s ∝-particle scattering experiment was responsible for the discovery of
(A) atomic nucleus
(B) electron
(C) proton
(D) neutron
Answer:
(A) atomic nucleus
On the basis of his experiment, Rutherford predicted that the central part of the atom is positively charged and is responsible for the mass of the atom. He called this part as atomic nucleus.
Question 4.
Which of the following is true for Rutherford’s model but not for Thomson’s model of an atom?
(A) An atom is electrically neutral.
(B) An atom contains many electrons.
(C) An atom has positive and negative parts.
(D) An atom contains a positively charged nucleus.
Answer:
(D) An atom contains a positively charged nucleus.
According to Rutherford’s model, an atom contains a positively charged nucleus around which the electrons revolve in well-defined circular orbit.
Question 5.
The alpha particle is also known as
(A) a sub-atomic particle.
(B) an unionised helium atom.
(C) a doubly-charged helium ion.
(D) a neutral particle.
Answer:
(C) a doubly-charged helium ion.
An alpha particle is a doubly-charged helium ion, i.e. He2+.
Question 6.
Consider the following diagram,
Which among the following statements about the given model of atom is correct?
(A) Considered the nucleus as positively charged.
(B) Established that the a-particles are two times as heavy as a hydrogen atom.
(C) Neutrons revolve around the nucleus of the atom.
(D) The given model of an atom represents Thomson’s model.
Answer:
(A) Considered the nucleus as positively charged.
The given model of atom represents Rutherford’s model. According to this model, a central positively charged nucleus is present in the atom and electrons revolve around it. This model is similar to solar system so also called planetary model.
Question 7.
Which formula is used to find the maximum number of electrons that can be accommodated in an orbit?
(A) 2n + 2
(B) 2 (n + 2)
(C) 2n/n2
(D) 2n2
Answer:
(D) 2n2
The formula 2n2 is used to find the maximum number of electrons in an orbit, where n is the shell number.
Question 8.
What is the maximum number of electrons that can be present in the first shell of an atom?
(A) 1
(B) 2
(C) 4
(D) 8
Answer:
(B) 2
The maximum number of electrons that can be present in the first shell.
n = 1
Maximum e– present is given by
2n2 = 2 × (1)2 = 2 where n is the shell number.
Question 9.
Which of the following is not true about Bohr and Bury’s rules for electronic configuration?
(A) The maximum number of electrons present in a shell is given by the formula 2n2.
(B) The maximum number of electrons present in a shell is given by the formula 2n.
(C) The maximum number of electrons that can be accommodated in the outermost shell is 8.
(D) Electrons are not accommodated in a given shell, unless the inner shells are completely filled.
Answer:
(B) The maximum number of electrons present in a shell is given by the formula 2n.
Statement (B) is not true about Bohr and Bury’s rule for electronic configuration because the maximum number of electrons present in a shell is given by the formula 2n2.
Question 10.
The discovery of radioactivity led to which of the following conclusions about the nature of atoms?
(A) Atoms are indivisible and cannot emit energy.
(B) Atoms are composed of smaller particles and can emit energy or radiation.
(C) Atoms consist only of protons and electrons arranged uniformly.
(D) Atoms are completely empty and contain no internal structure.
Answer:
(B) Atoms are composed of smaller particles and can emit energy or radiation.
The discovery of radioactivity revealed that atoms can emit energy and particles, indicating that they are not indivisible but possess an internal structure composed of subatomic particles.
Question 11.
Why was Thomson’s model of the atom eventually discarded?
(A) It could not explain the existence of electrons in atoms.
(B) It failed to account for the results of Rutherford’s gold foil experiment.
(C) It did not include the concept of atomic mass.
(D) It suggested that atoms are divisible.
Answer:
(B) It failed to account for the results of Rutherford’s gold foil experiment.
Thomson’s model was discarded because it could not explain the observations of Rutherford’s gold foil experiment, particularly the large deflection of some alpha particles, which indicated the presence of a small, dense, positively charged nucleus.
Question 12.
Match Column I with Column II.
| Column I | Column II |
| A. Maximum number of electrons in the K-shell. | (i) 2n2 |
| B. Electrons in the outermost shell of sodium. | (h) 2 |
| C. Maximum electrons in a shell. | (iii) 1 |
| D. Number of electrons in Cl– ion. | (iv) 18 |
(A) A-(ii), B-(iii), C-(i), D-(iv)
(B) A-(ii), B-(iv), C-(i), D-(iii)
(C) A-(iv), B-(i), C-(ii), D-(iii)
(D) A-(i), B-(ii), C-(iii), D-(iv)
Answer:
(A) The correct match is, A-(ii), B-(iii), C-(i), D-(iv).
Question 13.
The electronic configuration of two elements X and Y are 2, 8, 8, 2 and 2, 8, 3. Identify the elements X and Y respectively.
(A) X is calcium and Y is aluminium.
(B) X is copper and Y is sodium.
(C) X is silver and Y is silicon.
(D) X is palladium and Y is zinc.
Answer:
(A) X is calcium and Y is aluminium.
The given electronic configuration contains 20 and 13 electrons respectively.
Therefore, it is the electronic configuration of calcium and aluminium whose atomic numbers are 20 and 13.
Question 14.
The picture shows the arrangement of electrons in the shells of different atoms.
Which atom among the following has zero valency ?
(A) Atom 1
(B) Atom 2
(C) Atom 3
(D) Atom 4
Answer:
(C) Atom 3
Atom 3 has zero valency because it shows 2 electrons in its outermost shell, i.e. 2s2. It has a stable electronic configuration.
Question 15.
Rutherford’s model of the atom is often compared to which of the following?
(A) Plum pudding model
(B) Planetary model
(C) Solid sphere model
(D) Wave model
Answer:
(B) Planetary model
Rutherford’s atomic model is compared to the planetary model, as electrons revolve around the nucleus in paths similar to planets orbiting the Sun.
Question 16.
What would be the valency of an element that is chemically inactive?
(A) 0
(B) 1
(C) 2
(D) 5
Answer:
(A) 0
Chemically inactive elements like helium, neon, radon and argon etc. have zero valency because they have their outer shell completely filled, thus, have a stable electronic configuration.
Question 17.
Find out the valency of the atoms represented by the Fig. (1) and Fig. (2) given below
(A) 1 and 2 respectively
(B) 0 and 1 respectively
(C) 1 and 1 respectively
(D) 0 and 2 respectively
Answer:
(B) 0 and 1 respectively
The electronic configuration in Fig. (1) is 2, 8, 8. As its K, L, and M shells are completely filled, its valency will be zero. It is an inert gas, argon (Ar).
The electronic configuration in Fig. (2) is 2, 7. As,it has seven electrons in its valence shell, it can gain one electron to complete the octet, so its valency is one.
The atom belongs to the element fluorine (F).
Question 18.
What was the major limitation of Rutherford’s atomic model?
(A) It could not explain the presence of a nucleus in the atom.
(B) It failed to describe the distribution of positive charge.
(C) It could not explain the stability of atoms.
(D) It suggested that atoms are indivisible.
Answer:
(C) It could not explain the stability of atoms.
Rutherford’s model could not explain the stability of the atom, as according to science, an electron moving in a circular orbit should continuously lose energy and eventually collapse into the nucleus, which contradicts the existence of stable atoms.
Question 19.
The atomic number of an element is equal to
(A) number of neutrons
(B) number of electrons
(C) number of neutrons + number of protons
(D) number of protons
Answer:
(D) number of protons
The atomic number of an element is equal to number of protons.
Question 20.
When the atomic number of an element is increased by one, the change observed in the atom is because
(A) the number of protons decreases by one.
(B) one proton and one electron are added to the atom.
(C) only one neutron is added to the nucleus.
(D) one electron is removed from the atom.
Answer:
(B) one proton and one electron are added to the atom.
Atomic number represents the number of protons in an atom. Increasing the atomic number by one means one more proton (and to maintain neutrality, one electron) is added.
Question 21.
| Atoms | Mass number | Atomic number |
| A | 40 | 20 |
| B | 7 | 3 |
| C | 14 | 7 |
| D | 16 | 8 |
Which of these atoms contains 7 protons?
(A) A
(B) B
(C) C
(D) D
Answer:
(C) C
Proton count is equal to the atomic number of an element. Hence, atom C contains 7 protons.
Question 22.
Which of the following particles primarily contribute to the mass of an atom?
(A) Electrons only
(B) Protons only
(C) Protons and neutrons
(D) Neutrons and electrons
Answer:
(C) Protons and neutrons
The mass of an atom is primarily contributed by protons and neutrons present in the nucleus, as electrons possess negligible mass in comparison.
Question 23.
The atomic number of some elements is shown.
| Elements | Atomic numbers |
| Beryllium (Be) | 4 |
| Oxygen (O) | 8 |
| Silicon (Si) | 14 |
| Chlorine (Cl) | 17 |
Which elements have a valency of 2?
(A) Be and Si
(B) Si and Cl
(C) Be and O
(D) Cl and O
Answer:
(C) Be and O
The electronic configuration of the given elements are
Be = 2, 2
O = 2, 6
Si = 2, 8, 4
Cl = 2, 8, 7
Thus, among the given elements, Be and O have valency of 2.
Question 24.
Two elements P and Q have atomic numbers 11 and 17 respectively. Their electron distributions are studied.
Which of the following observations is correct?
| Sample | Electron distribution | Valency |
| (A) | P: 2, 8, 1; Q: 2, 8, 7 | P: 1; Q: 1 |
| (B) | P: 2, 8, 1; Q: 2, 8, 7 | P: 1; Q: 7 |
| (C) | P: 2, 8, 1; Q: 2, 7, 8 | P: 1; Q: 1 |
| (D) | P: 2, 8, 1; Q: 2, 8, 7 | P: 1; Q: 8 |
Answer:
(A) P: 2, 8, 1; Q: 2, 8, 7 | P: 1; Q: 1
Element P (Na, Z = 11) has valency 1 (loses 1 electron).
Element Q (Cl, Z = 17) has valency 1 (gains 1 electron to complete its octet).
Question 25.
Two students, P and Q, were asked to write the electron distribution of an element with atomic number 17.
- P wrote: 2, 8, 7
- Q wrote: 2, 7, 8
Which of the following is correct?
(A) Only P is correct.
(B) Only Q is correct.
(C) Both P and Q are correct.
(D) Neither P nor Q is correct.
Answer:
(A) Only P is correct.
An atom with atomic number 17 is chlorine, which has the electronic configuration like 2, 8, 7.
Question 26.
Who discovered the neutron, a neutral subatomic particle present in the nucleus of an atom?
(A) J. J. Thomson
(B) Ernest Rutherford
(C) James Chadwick
(D) Niels Bohr
Answer:
(C) James Chadwick
The neutron was discovered by James Chadwick in 1932, who identified it as a neutral particle with mass comparable to that of a proton, placed within the atomic nucleus.
Question 27.
Identify the Schematic atomic structure of Mg2+ ion from the figure where, n and p represent the number of neutrons and protons respectively.
(A) 
(B) 
(C) 
(D) 
Answer:
(D)
Electronic configuration of 12 Mg atom = 
and that of Mg2+ ion = 
i. e. In K-shell = 2 electrons
In L-shell = 8 electrons
Now, number of protons in Mg2+ atom = 2 + 8 = 10
Number of neutrons in Mg atom = 24 – 12 = 12
[as mass number of Mg atom = 24 and number of neutrons = mass number – number of protons]
Therefore, option (D) is the correct answer.
Question 28.
According to John Dalton’s 1803 nomenclature, which of the following pictorial symbols represents a Sulphur atom?
(A) 
(B) 
(C) 
(D) 
Answer:
(C)
According to Dalton’s pictorial symbols, sulphur is represented by a circle divided into four equal parts by a cross.
(a) Hydrogen (a simple circle with a dot inside)
(b) Phosphorus (circle divided into three sectors)
(c) Sulphur
(d) Carbon (represented by the letter “C” in modern notation, not Dalton’s original symbol).
Question 29.
The isotopes of chlorine with mass numbers 35 and 37 exists in the ratio of
(A) 3 : 1
(B) 1 : 3
(C) 1 : 2
(D) 2 : 1
Answer:
(A) 3 : 1
Chlorine occurs in nature as a mixture of two isotopes – chlorine-35 and chlorine-37.
Their natural abundance ratio is 3 : 1, meaning that out of every four atoms of chlorine, three are chlorine-35 and one is chlorine-37.
Question 30.
The element Oxygen has an atomic number of 8 and a mass number of 16. Its chemical symbols is O. According to standard chemical notation, which of the following is the correctly way to represent this oxygen atom?
(A) \({ }_{16}^{8} O\)
(B) \({ }_8^{16} O\)
(C) \(\mathrm{O}_8^{16}\)
(D) 16O8
Answer:
(B) \({ }_8^{16} O\)
The correct representation of an atom follows the notation \({ }_Z^{A} X\), where A (mass number is written as a superscript and Z (atomic number) as a subscript. Therefore, oxygen is correctly represented as \({ }_8^{16} O\), making option (b) the correct choice.
Question 31.
Which radioactive element is used in the treatment of cancer?
(A) Iodine-131
(B) Uranium-234
(C) Plutonium-239
(D) Cobalt-60
Answer:
(D) Cobalt-60
Cobalt-60 is a radioactive element which is used in the treatment of cancer.
Question 32.
Which isotope of carbon is commonly used to determine the age of ancient fossils and artefacts?
(A) Carbon-12
(B) Carbon-13
(C) Carbon-14
(D) Carbon-16
Answer:
(C) Carbon-14
Carbon-14 is a radioactive isotope used in radiocarbon dating to estimate the age of ancient fossils and artefacts, owing to its predictable rate of decay.
Question 33.
Which of the following atoms are isobars?
(A) \({ }_6^{12} C\) and \({ }_6^{14} C\)
(B) \({ }_6^{14} C\) and \({ }_{18}^{40} Ar\)
(C) \({ }_{18}^{40} Ar\) and \({ }_{20}^{40} Ca\)
(D) \({ }_3^{6} Li\) and \({ }_6^{12} C\)
Answer:
(C) \({ }_{18}^{40} Ar\) and \({ }_{20}^{40} Ca\)
Atoms of different elements with different atomic numbers but same mass number are known as isobars. Thus, \({ }_{18}^{40} Ar\) and \({ }_{20}^{40} Ca\) are isobars having mass number 40.
Question 34.
Four statements about atomic structure and isotopes are listed.
i. In Rutherford’s a-particle scattering experiment, most of the a-particles passed undeflected because the atom is mostly empty space.
ii. Isotopes of an element have the same number of protons but different number of neutrons.
iii. According to Bohr’s model, electrons revolve in specified orbits called energy shells without emitting energy.
iv. Isobars are atoms of different elements having the same number of nucleons but different atomic numbers.
Which statements are correct?
(A) i and ii only
(B) i, ii and iii only
(C) i, ii, iii and iv
(D) ii, iii and iv only
Answer:
(C) i, ii, iii and iv.
Most α-particles passed undeflected as the atom has largely an empty space. Isotopes have the same number of protons but different number of neutrons. Electrons revolve in fixed orbits without radiating energy. Isobars have the same mass number but different atomic numbers
Question 35.
Which of the following model describes the structure of an atom proposed by Thomson?
(A) 
(B) 
(C) 
(D) 
Answer:
(A)
This model describes Thomson’s model of atoms in which electrons are embedded in a sphere of positive charge (like seeds in a watermelon).
Question 36.
How many neutrons are present in the nucleus of hydrogen atom?
(A) 1
(B) 2
(C) 3
(D) 0
Answer:
(D) 0
Hydrogen has no neutrons.
Question 37.
Which of the following correctly represent the electronic distribution in the Mg atom ?
(A) 2, 8, 1
(B) 2, 8, 2
(C) 1,8, 2
(D) 8, 2, 2
Answer:
(B) 2, 8, 2
The correct electronic distribution is 2,8,2 (Mg has 12 electrons total).
Question 38.
Which of the following is an accurate illustration of a nitrogen atom?
(A) 
(B) 
(C) 
(D) 
Answer:
(A)
This illustration shows 2 electrons in the first shell and 5 in the outer shell (configuration 2, 5).
Question 39.
The number of electrons in an element X is 15 and the number of neutrons is 16. Which of the following is the correct representation of the element?
(A) \({ }_{15}^{31} X\)
(B) \({ }_{16}^{31} X\)
(C) \({ }_{15}^{16} X\)
(D) \({ }_{16}^{15} X\)
Answer:
(A) \({ }_{15}^{31} X\)
The atomic number is 15 (electrons = protons) and the mass number is 31 (15 protons + 16 neutrons).
Question 40.
The ion of an atom has 2 negative charges. Mass number of the atom is 16 and the number of neutrons are 8. What is the number of electrons in the ion?
(A) 6
(B) 7
(C) 8
(D) 10
Answer:
(D) 10
The number of electrons in the ion is 10 because of 2 negative charges on the ion.
Journey Inside the Atom Class 9 Assertion and Reason Questions
Direction (Question Nos. 1 – 11): The following questions consist of two statements-Asssertion (A) and Reason (R):. Answer these questions by selecting the appropriate option given below.
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
(C) Assertion is true, but Reason is false.
(D) Assertion is false, but Reason is true.
Question 1.
Assertion (A): Atom is electrically neutral.
Reason (R): A neutral particle, i.e. neutron, is present in the nucleus of an atom.
Answer:
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
Because of the presence of equal number of protons and electrons, the atom is electrically neutral. Protons and neutrons collectively called as nucleons and are present in the nucleus of the atom. Hence, both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Question 2.
Assertion (A): Thomson’s atomic model was rejected after Rutherford’s gold foil experiment.
Reason (R): Thomson’s model could not explain the existence of a small, dense, positively charged nucleus.
Answer:
(A) Both Assertion and Reason are true and the Reason correctly explains the Assertion.
Thomson’s model failed to account for the dense, positively charged nucleus experimentally determined by Rutherford’s experiment.
Question 3.
Assertion (A): In Rutherford’s gold foil experiment, very few α-particles are deflected back.
Reason (R): Nucleus present inside the atom is heavy.
Answer:
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
The nucleus is indeed heavy, but very few α-particles are deflected back because the nucleus occupies a very small space within the atom.
Hence, both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Question 4.
Assertion (A): Rutherford compared his atomic model to a planetary model.
Reason (R): Electrons revolve around the nucleus in circular paths like planets around the Sun.
Answer:
(A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
While Rutherford’s model is compared to a planetary model, accordingly electrons revolves around the nucleus just like planets revolve around sun.
Question 5.
Assertion (A): Anions are larger in size than the parent atom.
Reason (R): In an anion, the number of protons in the nucleus is less than the number of electrons moving around it.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Anion has more electrons as compared to protons in an atoms. It is formed when an atom gains one or more electrons. Therefore, anions are larger in size. Hence, Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Question 6.
Assertion (A): The atomic masses of some elements are in fractions and not a whole numbers.
Reason (R): The fractional atomic masses of some elements are due to the existence of their isotopes having different masses.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
The atomic mass is weighed average of the masses of all naturally occuring isotopes, which often results in fractional value.
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Question 7.
Assertion (A): The mass of an atom is mainly concentrated in its nucleus.
Reason (R): Electrons contribute significantly to the mass of an atom.
Answer:
(C) Assertion is true, but Reason is false.
The mass of an atom is concentrated in the nucleus, whereas electrons contribute negligibly to the atomic mass.
Question 8.
Assertion (A): Chlorine has a valency of one.
Reason (R): One atom of chlorine combines with one atom of hydrogen to form HCl.
Answer:
(A) Both Assertion and Reason are true, and the Reason correctly explains the Assertion.
Chlorine exhibits a valency of one as it combines with one hydrogen atom to form HCL
Question 9.
Assertion (A): Bohr’s orbits are called stationary orbits.
Reason (R): Electrons remain stationary in these orbits for sometime.
Answer:
(C) Assertion is true, but Reason is false.
Bohr’s orbits are stationary because electrons don’t radiate energy in them, not because they remain physically stationary. Hence, Assertion is true but Reason is false.
Question 10.
Assertion (A): The maximum number of electrons that can be accommodated in a shell is given by the formula 2n2, where n is the shell number.
Reason (R): The shells are filled in the order K, L, M, N according to their increasing energy levels.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Orbits are called energy levels because each has a fixed, definite energy value. Hence, both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Question 11.
Assertion (A): The valency of an atom of fluorine is 7.
Reason (R): The number of electrons present in the outermost shell of fluorine atom is 7.
Answer:
(D) Assertion is false, but Reason is true.
A fluorine atom has 7 electrons in its outermost shell (2, 7), so it needs 1 more electron to complete its octet. Therefore, its valency is 1, not 7.