Question

Smallest among these species is:

• A. Lithium
• B. Lithium ion
• C. Hydrogen
• D. Helium

Answer 1

Answer: (C)

Hydrogen

The electronic configuration of these elements is as follows:
Hydrogen : $1s^1$

Helium:$1s^2$

Lithium:$1s^{2}2s^1$

Lithium ion:$1s^2$

Three of the elements have one orbital and since hydrogen has only one electron, it is smallest among all the species.