Unit 1: Basic concepts Chemistry

41. The element with the electron configuration 1s² 2s² 2p⁵ is:

a) Oxygen
b) Nitrogen
c) Fluorine
d) Neon
Answer: c) Fluorine

42. In the context of atomic theory, the term “quantum” refers to:

a) The energy level of an electron
b) The charge of an electron
c) The mass of an electron
d) The number of protons in the nucleus
Answer: a) The energy level of an electron

43. The principle stating that it is impossible to know both the position and momentum of an electron simultaneously is known as:

a) The Pauli exclusion principle
b) The Heisenberg uncertainty principle
c) Hund’s rule
d) The Aufbau principle
Answer: b) The Heisenberg uncertainty principle

44. The term used to describe the orbitals in which electrons are found is:

a) Energy levels
b) Electron clouds
c) Shells
d) Subshells
Answer: d) Subshells

45. The concept of quantized energy levels in atoms was introduced by:

a) Niels Bohr
b) Ernest Rutherford
c) J.J. Thomson
d) James Chadwick
Answer: a) Niels Bohr

46. Which of the following elements has the highest ionization energy?

a) Sodium
b) Magnesium
c) Chlorine
d) Argon
Answer: d) Argon

47. The concept of atomic mass unit (amu) is based on the mass of which isotope?

a) Carbon-12
b) Hydrogen-1
c) Oxygen-16
d) Uranium-238
Answer: a) Carbon-12

48. In the periodic table, elements with similar chemical properties are found in the same:

a) Period
b) Group
c) Block
d) Series
Answer: b) Group

49. The maximum number of electrons that can occupy an s orbital is:

a) 1
b) 2
c) 4
d) 6
Answer: b) 2

50. The element with an electron configuration ending in 3d⁵ 4s² is:

a) Iron
b) Cobalt
c) Nickel
d) Copper
Answer: a) Iron