Question

In $4^{\text{th}}$ period of periodic table the elements with the largest and smallest size respectively is :

• A. K and Br
• B. Na and Cl
• C. K and Se
• D. Rb and Br

Hint:

Size Trend: Alkali Metal > Alkaline Earth > ... > Halogen.

Answer 1

The Correct Option is A

In the 4th period (K to Kr):
Atomic radius decreases across the period from left to right.
Largest atom: Alkali Metal $\to$ Potassium (K).
Smallest atom: Halogen $\to$ Bromine (Br). (Noble gases have larger van der Waals radii, so typically halogens are considered smallest in covalent radius trends).
Option (1) K and Br is the correct pair.