Question

Name the element that belongs to s-block but is placed in the p-block.

(a) Hydrogen

(b) Helium

(c) Argon

(d) Aluminum

The question was asked during an internship interview.

This question is from Electronic Configurations and Types of Elements: s, p, d and f Blocks in portion Classification of Elements and Periodicity in Properties of Chemistry – Class 11

Answer 1

Correct choice is (b) Helium

Easy explanation: Helium’s electronic configuration is 1s^2. As the last electron is filled in s-orbital, it belongs to s-block. Since the 1^st shell cannot accommodate any orbital than s, 1s^2 is completely filled orbital, hence making it, a noble gas. Noble gases are placed in p-block.