Question

Atomic numbers of few elements are given below. Which of the pairs belongs to s-block?

• A. 7,14
• B. 3,20
• C. 8,15
• D. 9,17

Answer 1

Answer: (B)

3,20


Atomic numbers 3, 20 belongs to s-block.

The element with $Z=3$ and electronic configuration $1s^{2}2s^1;$ is an alkali metal.

The element with $Z=20$ and electronic configuration $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^2$ is an alkaline earth metal.