Atoms

PYQ-Based Questions (Q1–10)

Who proposed the atomic theory in the early 19th century? (BPSC 66th Prelims)
a) J.J. Thomson
b) John Dalton
c) Niels Bohr
d) Ernest Rutherford
Answer: b
Explanation: John Dalton proposed the modern atomic theory in 1808, which laid the foundation for understanding atomic structure.
Which of the following particles has no charge? (UPSC CDS 2019)
a) Proton
b) Electron
c) Neutron
d) Positron
Answer: c
Explanation: Neutrons are neutral particles found in the nucleus; they have no charge.
What is the mass of a proton? (BPSC 64th Prelims)
a) 1 amu
b) 0 amu
c) 4 amu
d) 0.0005 amu
Answer: a
Explanation: The mass of a proton is approximately 1 atomic mass unit (amu).
Who discovered the nucleus of an atom? (BPSC 60-62nd Prelims)
a) Bohr
b) Rutherford
c) Thomson
d) Dalton
Answer: b
Explanation: Rutherford's gold foil experiment led to the discovery of the atomic nucleus.
Which of the following is negatively charged? (BPSC 67th Prelims)
a) Neutron
b) Proton
c) Electron
d) Alpha particle
Answer: c
Explanation: Electrons carry a negative charge and orbit the nucleus.
Which model suggested that electrons revolve in fixed orbits? (UPSC Prelims 2013)
a) Dalton's model
b) Thomson's model
c) Rutherford's model
d) Bohr's model
Answer: d
Explanation: Niels Bohr proposed that electrons move in fixed orbits around the nucleus.
Which of the following is a fundamental particle of an atom? (MPPSC 2020)
a) Electron
b) Photon
c) Meson
d) Boson
Answer: a
Explanation: Electrons are fundamental subatomic particles found in all atoms.
What is the charge on an alpha particle? (UPPSC 2018)
a) +1
b) +2
c) -1
d) 0
Answer: b
Explanation: An alpha particle consists of 2 protons and 2 neutrons, giving it a +2 charge.
Which of the following is used to determine atomic number? (BPSC 68th Prelims)
a) Number of electrons
b) Number of neutrons
c) Number of protons
d) Mass number
Answer: c
Explanation: Atomic number is defined as the number of protons in the nucleus.
What was the major flaw in Rutherford’s model? (UPSC NDA 2016)
a) It couldn't explain the stability of atoms
b) It ignored protons
c) It denied the existence of electrons
d) It predicted a neutral nucleus
Answer: a
Explanation: According to classical physics, electrons would spiral into the nucleus, making the atom unstable, which contradicted observations.

NCERT-Based Questions (Q11–30)

Which subatomic particle determines the chemical properties of an element?
a) Neutron
b) Proton
c) Electron
d) Nucleus
Answer: c
Explanation: Chemical properties are determined by the arrangement and number of electrons, especially in the outermost shell.
Atomic number is defined as:
a) Number of electrons
b) Number of neutrons
c) Number of protons
d) Mass number
Answer: c
Explanation: Atomic number = number of protons = number of electrons in a neutral atom.
Isotopes are atoms with:
a) Same number of protons but different number of neutrons
b) Same number of neutrons but different protons
c) Same atomic and mass numbers
d) Different atomic numbers
Answer: a
Explanation: Isotopes have the same atomic number (same element) but different mass numbers due to varying neutrons.
Mass number is the sum of:
a) Protons and neutrons
b) Electrons and protons
c) Neutrons and electrons
d) Electrons only
Answer: a
Explanation: Mass number = total number of protons + neutrons.
Which of these particles is the lightest?
a) Proton
b) Neutron
c) Electron
d) Nucleus
Answer: c
Explanation: Electron has negligible mass compared to protons and neutrons.
What is the charge on a proton?
a) +1
b) -1
c) 0
d) +2
Answer: a
Explanation: Protons are positively charged.
What is the approximate size of an atom?
a) 1 meter
b) 1 millimeter
c) 10^-10 meters
d) 10^-6 meters
Answer: c
Explanation: Atomic radius is typically in the order of 10^-10 meters (1 angstrom).
Which scientist first used the term ‘atomos’?
a) Dalton
b) Democritus
c) Bohr
d) Newton
Answer: b
Explanation: Greek philosopher Democritus introduced the idea of indivisible particles called "atomos."
The total number of electrons in a neutral atom is equal to:
a) Number of neutrons
b) Number of protons
c) Mass number
d) Number of nuclei
Answer: b
Explanation: In a neutral atom, electrons = protons.
Which of these models described atoms as indivisible hard spheres?
a) Thomson
b) Rutherford
c) Bohr
d) Dalton
Answer: d
Explanation: Dalton's model viewed atoms as solid, indivisible spheres.
What is the main limitation of Dalton's theory?
a) Atoms are indivisible
b) Atoms have internal structure
c) Atoms are unreactive
d) Atoms do not exist
Answer: b
Explanation: Later discoveries showed that atoms are divisible into subatomic particles.
What did Thomson's model propose?
a) Electrons are outside nucleus
b) Electrons embedded in positive sphere
c) Atom is indivisible
d) Atoms are empty
Answer: b
Explanation: The "plum pudding model" had electrons embedded in a positively charged sphere.
Who discovered the electron?
a) J.J. Thomson
b) Rutherford
c) Neils Bohr
d) Chadwick
Answer: a
Explanation: J.J. Thomson discovered the electron in 1897 through cathode ray experiments.
Which particle was discovered by Chadwick?
a) Proton
b) Electron
c) Neutron
d) Positron
Answer: c
Explanation: James Chadwick discovered the neutron in 1932.
Which force binds protons and neutrons in the nucleus?
a) Gravitational force
b) Nuclear force
c) Magnetic force
d) Electrostatic force
Answer: b
Explanation: The strong nuclear force holds nucleons together in the nucleus.
Which subatomic particle revolves in orbits?
a) Proton
b) Electron
c) Neutron
d) Nucleon
Answer: b
Explanation: Electrons revolve in fixed orbits around the nucleus.
Which is a positively charged subatomic particle?
a) Electron
b) Neutron
c) Proton
d) Meson
Answer: c
Explanation: Protons have a +1 charge.
Which of the following does NOT change in isotopes?
a) Neutron number
b) Mass number
c) Proton number
d) Atomic mass
Answer: c
Explanation: Isotopes of an element have the same proton number (atomic number).
Which is not a subatomic particle?
a) Electron
b) Proton
c) Neutron
d) Molecule
Answer: d
Explanation: A molecule is made of atoms, not a part of an atom.
What does the atomic mass unit (amu) measure?
a) Energy
b) Charge
c) Mass of particles
d) Volume
Answer: c
Explanation: Atomic mass unit is used to express the mass of subatomic particles.

Predicted/Reference Book-Based Questions (Q31–50)

Who proposed the planetary model of the atom?
a) Bohr
b) Rutherford
c) Dalton
d) Thomson
Answer: b
Explanation: Rutherford’s gold foil experiment led to the planetary model of the atom.
What is the charge of the nucleus?
a) Neutral
b) Positive
c) Negative
d) Varies
Answer: b
Explanation: The nucleus contains positively charged protons and neutral neutrons.
In which model were energy levels introduced?
a) Dalton’s model
b) Thomson’s model
c) Rutherford’s model
d) Bohr’s model
Answer: d
Explanation: Bohr introduced the concept of discrete energy levels for electrons.
Which subatomic particle is responsible for bonding?
a) Proton
b) Neutron
c) Electron
d) Nucleus
Answer: c
Explanation: Electrons, particularly valence electrons, are involved in chemical bonding.
Mass number of an element is:
a) Equal to atomic number
b) Equal to electrons + protons
c) Equal to protons + neutrons
d) Always the same as atomic number
Answer: c
Explanation: Mass number is the total of protons and neutrons in an atom.
Hydrogen has how many protons?
a) 0
b) 1
c) 2
d) 3
Answer: b
Explanation: Hydrogen has 1 proton and 0 neutrons.
Which particle is common in all atoms?
a) Proton
b) Neutron
c) Electron
d) All of these
Answer: a
Explanation: Protons define the atomic number and are present in all atoms.
The concept of shells or energy levels is best explained by:
a) Dalton
b) Rutherford
c) Bohr
d) Thomson
Answer: c
Explanation: Bohr introduced shells like K, L, M to describe electron arrangement.
The number of shells in an atom is called:
a) Atomic number
b) Period
c) Group
d) Orbitals
Answer: b
Explanation: The number of shells corresponds to the period of the element in the periodic table.
Which element has no neutrons?
a) Helium
b) Oxygen
c) Hydrogen
d) Lithium
Answer: c
Explanation: Most hydrogen atoms have only 1 proton and no neutrons.
What is the atomic number of carbon?
a) 6
b) 12
c) 14
d) 4
Answer: a
Explanation: Carbon has 6 protons.
What is the full form of AMU?
a) Atomic Mass Unit
b) Atomic Molecular Unit
c) Atomic Mole Unit
d) Atom Meter Unit
Answer: a
Explanation: AMU stands for Atomic Mass Unit.
Which of these models resembles a solar system?
a) Dalton
b) Thomson
c) Bohr
d) Rutherford
Answer: d
Explanation: Rutherford's model resembles the solar system with electrons orbiting the nucleus.
Which is the heaviest subatomic particle?
a) Electron
b) Proton
c) Neutron
d) Positron
Answer: c
Explanation: Neutron is slightly heavier than the proton.
Which particle defines the identity of an atom?
a) Neutron
b) Electron
c) Proton
d) Quark
Answer: c
Explanation: The number of protons determines the element’s identity.
What is the maximum number of electrons in the first shell?
a) 2
b) 8
c) 18
d) 32
Answer: a
Explanation: The first shell (K) can hold a maximum of 2 electrons.
What is the total charge on a neutral atom?
a) Positive
b) Negative
c) Zero
d) Varies
Answer: c
Explanation: In neutral atoms, total positive charge = total negative charge.
What is the number of neutrons in Carbon-14?
a) 6
b) 7
c) 8
d) 14
Answer: c
Explanation: Carbon-14 has 6 protons and 8 neutrons (14 – 6 = 8).
The smallest unit of matter is:
a) Molecule
b) Atom
c) Cell
d) Electron
Answer: b
Explanation: Atom is the smallest unit of a chemical element.
What is the name of the positively charged ion?
a) Cation
b) Anion
c) Proton
d) Isotope
Answer: a
Explanation: Cation is a positively charged ion formed by the loss of electrons.