The following 20 Multiple Choice Questions (MCQ) are based on
Chapter 8: Journey Inside the Atom from the NCERT Class 9
Science textbook Exploration. Each question has four options - select the
best answer and click to check.
Instructions: Read each question carefully. Choose the most
appropriate option from (a), (b), (c), or (d). Click
Show Answer to reveal the correct answer with explanation.
Multiple Choice Questions
1Which statement about an atom is correct?
(a) It has no internal structure
(b) It contains subatomic particles
(c) It is visible to the naked eye
(d) All atoms have identical mass
(b) is correct
Atoms contain electrons, protons and usually neutrons.
2In Thomson's model, the atom was pictured as:
(a) A positive sphere with electrons embedded in it
(b) A solid indivisible cube
(c) Electrons in fixed shells around a tiny nucleus
(d) Only a neutron cloud
(a) is correct
Thomson proposed electrons embedded in a uniformly positive charge.
3Rutherford's gold foil experiment used:
(a) Beta particles and iron foil
(b) Alpha particles and thin gold foil
(c) Sound waves and silver
(d) Neutrons and paper
(b) is correct
Alpha particles were directed at extremely thin gold foil to probe atomic structure.
4Most alpha particles passed straight through gold foil, showing that an atom is mostly:
(a) Positive charge
(b) Empty space
(c) Solid matter
(d) Neutrons
(b) is correct
The large unoccupied region allowed most particles to pass with little deflection.
5The rare large deflections in Rutherford's experiment indicated a:
(a) Diffuse negative centre
(b) Small, dense, positively charged nucleus
(c) Uniformly filled atom
(d) Massless atom
(b) is correct
Strong repulsion could occur only near a concentrated positive nucleus.
6A limitation of Rutherford's model was that it could not explain:
(a) The existence of a nucleus
(b) Atomic stability and electron arrangement
(c) That atoms contain mass
(d) Alpha-particle charge
(b) is correct
Classical orbiting electrons should lose energy, so the model could not account for stable atoms.
7Bohr proposed that electrons occupy:
(a) Any position with any energy
(b) Specific energy levels or shells
(c) The nucleus
(d) Only one universal orbit
(b) is correct
Allowed shells have definite energies, helping explain atomic stability.
8Which subatomic particle has a negative charge?
(a) Proton
(b) Neutron
(c) Electron
(d) Nucleus
(c) is correct
An electron carries one unit of negative charge.
9Which particle determines an element's atomic number?
(a) Neutron
(b) Proton
(c) Electron shell
(d) Isotope
(b) is correct
Atomic number Z equals the number of protons in the nucleus.
10A neutral atom with atomic number 8 has how many electrons?
(a) 4
(b) 8
(c) 16
(d) 10
(b) is correct
A neutral atom has equal numbers of protons and electrons.
11Mass number equals the total number of:
(a) Electrons and protons
(b) Protons and neutrons
(c) Neutrons and shells
(d) Valence electrons only
(b) is correct
A = number of protons + number of neutrons.
12An atom has 11 protons and 12 neutrons. Its mass number is:
(a) 1
(b) 11
(c) 12
(d) 23
(d) is correct
Mass number = 11 + 12 = 23.
13The maximum number of electrons in the first shell is:
(a) 1
(b) 2
(c) 8
(d) 18
(b) is correct
Using 2n^2 for n = 1 gives a capacity of 2 electrons.
14The electron configuration of sodium (atomic number 11) is:
(a) 2, 8, 1
(b) 2, 7, 2
(c) 8, 3
(d) 2, 9
(a) is correct
Eleven electrons fill the shells as 2, 8 and 1.
15Valence electrons are located in the:
(a) Nucleus
(b) Outermost occupied shell
(c) First shell only
(d) Neutron
(b) is correct
The outermost electrons mainly determine combining behaviour.
16The usual valency of an atom with seven valence electrons is:
(a) 0
(b) 1
(c) 2
(d) 7
(b) is correct
It tends to gain one electron to complete an octet.
17Noble gases are generally unreactive because they have:
(a) No nucleus
(b) A complete outer shell
(c) Only one proton
(d) No electrons
(b) is correct
A filled valence shell is particularly stable.
18Isotopes are atoms of the same element with the same:
(a) Mass number but different atomic numbers
(b) Atomic number but different mass numbers
(c) Number of neutrons and protons
(d) Physical state only
(b) is correct
They have the same proton number but different neutron numbers.
19Which pair represents isotopes?
(a) Carbon-12 and carbon-14
(b) Carbon-14 and nitrogen-14
(c) Sodium-23 and magnesium-24
(d) Hydrogen-1 and helium-4
(a) is correct
Both are carbon atoms, but their neutron counts and mass numbers differ.
20Isobars have the same:
(a) Atomic number
(b) Mass number
(c) Number of electrons only
(d) Chemical symbol
(b) is correct
Isobars belong to different elements but share a mass number.
