Question

The elements A, B, C, D and E have atomic numbers 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group?

• A. A and B
• B. B and D
• C. A and C
• D. D and E

Answer 1

The correct option is C

A and C

The explanation for the correct option

(C) A and C

Electronic configuration

• The distribution of electrons into orbitals of an atom is called its electronic configuration.
• The electronic configuration of element A is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^5$.
• The electronic configuration of element B is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^1$.
• The electronic configuration of element C is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^5$.
• The electronic configuration of element D is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$.
• The electronic configuration of element E is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^1$.

Group

• The vertical columns in the periodic table are referred to as groups.
• The elements belonging to the same group have the same number of valence electrons.
• In elements A and C, seven valence electrons are present.
• So, pairs of elements belonging to the same group are A and C.

The explanation for the incorrect option

The pairs of elements belonging to the same group are A and C. Hence, options (A), (B), and (D) are incorrect.

Hence, the correct option is (C). The pair of elements belonging to the same group are A and C.