31. The concept of quantized energy levels in an atom was introduced by:

a) Niels Bohr
b) J.J. Thomson
c) Ernest Rutherford
d) Albert Einstein
Answer: a) Niels Bohr

32. In which experiment was the nucleus of an atom discovered?

a) Gold foil experiment
b) Cathode ray experiment
c) Oil drop experiment
d) Double-slit experiment
Answer: a) Gold foil experiment

33. The probability distribution of an electron is described by:

a) Newton’s laws
b) Wave function
c) Classical mechanics
d) Rutherford model
Answer: b) Wave function

34. Which quantum number indicates the shape of an orbital?

a) Principal quantum number
b) Azimuthal quantum number
c) Magnetic quantum number
d) Spin quantum number
Answer: b) Azimuthal quantum number

35. An atom becomes a cation by:

a) Gaining electrons
b) Losing electrons
c) Gaining protons
d) Losing protons
Answer: b) Losing electrons

36. Which of the following statements about the atomic nucleus is false?

a) It contains protons and neutrons
b) It is positively charged
c) It is very small compared to the atom
d) It contains all the electrons
Answer: d) It contains all the electrons

37. What is the shape of the p orbital?

a) Spherical
b) Dumbbell
c) Circular
d) Linear
Answer: b) Dumbbell

38. Which rule states that electrons fill the lowest energy orbitals first?

a) Hund’s Rule
b) Aufbau Principle
c) Pauli Exclusion Principle
d) Dalton’s Law
Answer: b) Aufbau Principle

39. The region of space around the nucleus where an electron is likely to be found is called:

a) Orbit
b) Orbital
c) Shell
d) Subshell
Answer: b) Orbital

40. Which of the following is a characteristic of electrons in the same orbital?

a) Same spin
b) Opposite spin
c) Different energy levels
d) Different atomic numbers
Answer: b) Opposite spin