Select the most appropriate option to fill in the blank.
He decided not to go for the picnic as he was feeling a little____________.

Correct option is B

The correct option to fill in the blank is (b) under the weather.
Explanation: The idiom under the weather means feeling unwell or sick. (Hindi: बीमार महसूस करना)
Example: I didn't attend the meeting today because I was feeling under the weather.
Meanings of other options and why they are incorrect:
· (a) As right as rain – In perfect health or condition. (बिल्कुल ठीक)
· (c) Head in the clouds – Daydreaming or not paying attention. (कल्पनाओं में खोया हुआ)
· (d) Calm before the storm – A quiet period before trouble begins. (तूफ़ान से पहले की शांति)
• Hence, only (b) fits the context of feeling unwell.