Which of the following are isobars?
a) ⁴⁰Ar₁₈, ⁴⁰K₁₉, ⁴⁰Ca₂₀
b) ⁴⁰Ar₁₈, ⁴²Ca₂₀, ⁴²K₁₉
c) ⁴¹Ar₁₈, ⁴¹K₁₉, ⁴¹Ca₂₀
d) None of the above
Answer: a
The order of orbital filling in atoms is governed by:
a) Aufbau principle
b) Heisenberg uncertainty principle
c) Hund’s rule
d) Pauli’s exclusion principle
Answer: a
When electrons in metal atoms fall back to lower energy levels after excitation, they emit:
a) Raman spectrum
b) Absorption spectrum
c) Emission spectrum
d) Fluorescence
Answer: c
Which statements about Bohr’s atomic model are correct?
– Introduces stationary orbits
– Assumes quantized angular momentum
– Uses planetary circular orbit model
a) 1 and 2
b) 2 and 3
c) 1 and 3
d) All of the above
Answer: d
The atomic size is roughly of the order of:
a) 10⁻⁸ cm
b) 10⁻¹⁰ cm
c) 10⁻¹³ cm
d) 10⁻⁶ cm
Answer: b
Which statement is incorrect about X-rays?
a) They are of low energy
b) They travel at the speed of light
c) They can be refracted
d) They affect photographic plates
Answer: a
Nuclear size is measured in:
a) amu
b) Angstrom
c) cm
d) Fermi
Answer: d
Which of these elements has exactly two electrons in its K-shell?
a) Hydrogen
b) Helium
c) Neon
d) Sulphur
Answer: b
The nucleus of an atom contains:
a) Only protons
b) Only neutrons
c) Protons and neutrons
d) Electrons, protons, and neutrons
Answer: c
Atomic mass number is calculated by:
a) Number of protons
b) Number of neutrons
c) Protons + Neutrons
d) Number of electrons
Answer: c
Which of the following is NOT a nucleon?
a) Proton
b) Electron
c) Neutron
d) Positron
Answer: b
Number of neutrons in a hydrogen atom is:
a) 1
b) 0
c) 2
d) 3
Answer: b
What does a helium atom become after losing both electrons?
a) Proton
b) He⁺ ion
c) He⁻ ion
d) Alpha particle
Answer: d
Which particle carries a negative charge?
a) Proton
b) Neutron
c) Positron
d) Electron
Answer: d
The absolute charge of an electron was determined by:
a) J.J. Thomson
b) R.A. Millikan
c) Rutherford
d) Chadwick
Answer: b
Electrons revolve around the nucleus in:
a) Straight lines
b) Spin motion
c) Orbitals
d) Vibrational motion
Answer: c
An atom has 2 electrons in K-shell, 8 in L-shell, and 8 in M-shell. Total number of s-electrons is:
a) 6
b) 5
c) 7
d) 10
Answer: d
A proton is heavier than an electron by approximately:
a) 187 times
b) 1835 times
c) 3837 times
d) 2827 times
Answer: b
CN⁻ ion is isoelectronic with:
a) N₂
b) CO
c) Both a & b
d) None
Answer: c
Maximum number of electrons that can be accommodated in the M-shell is:
a) 2
b) 8
c) 18
d) 32
Answer: c
Which of the following will be a negative ion (anion)?
a) More electrons than protons
b) More electrons than neutrons
c) More protons than electrons
d) More protons than neutrons
Answer: a
Electrons in the outermost shell of an atom are called:
a) Valence protons
b) Orbital protons
c) Valence electrons
d) Core electrons
Answer: c
Iron has 26 protons. What is the number of electrons in Fe²⁺?
a) 24
b) 26
c) 28
d) 13
Answer: a
The mass number of an atom is:
a) Always less than atomic number
b) Always more than atomic number
c) Always equal to atomic number
d) Sometimes more, sometimes equal
Answer: d
If r is the radius of the first orbit, the radius of the nth orbit in hydrogen is:
a) r × n²
b) r × n
c) r / n
d) r² × n²
Answer: a