Question

arrange the elements in the third period in order of decreasing atomic radius. (big to small)
sodium, phosphorus

Explanation:

Step1: Recall atomic - radius trend

Atomic radius decreases across a period from left to right due to increasing nuclear charge pulling electrons closer.

Step2: Identify positions in period 3

Sodium (Na) is on the left - hand side, and phosphorus (P) is more towards the right in the third period.

Step3: Add another element

Let's consider sulfur (S) which is also in the third period and to the right of phosphorus.

Answer:

Sodium > Phosphorus > Sulfur