Question

Identify the alkali metal having the smallest atomic size from following.

• A. Sodium
• B. Potassium
• C. Rubidium
• D. Caesium

Hint:

Atomic size increases down a group, so pick the highest element listed.

Answer 1

The Correct Option is A

Step 1: Locate the elements:
Na, K, Rb and Cs belong to Group 1. They sit in periods 3, 4, 5 and 6 respectively.

Step 2: Use the trend:
One more shell is added each period, and this outweighs the rise in nuclear charge. Radius therefore increases down the group.

Step 3: Pick:
The smallest radius belongs to the element in the lowest period number, which is sodium.

Final Answer:
Sodium has the fewest shells, hence the smallest size. \[ \boxed{A} \]