kaarbṛṇāyan hai - kṣār nābhik snehī (A) v (B) donoṁ koī nahīṁ.

The correct answer is (C).

To understand why, let's break it down:

1. कार्बऋणायन (Carbanion) is a molecule that contains a carbon atom with a negative charge.
2. क्षार (Base) is a substance that can accept protons (H⁺) or donate an electron pair.
3. नाभिक स्नेही (Nucleophile) is a chemical species that donates an electron pair to an electrophile to form a chemical bond in reaction.

Given these definitions:

• A carbanion is indeed a base because it can accept a proton due to its negative charge.
• It is also a nucleophile because it can donate its lone pair of electrons during a chemical reaction.

Therefore, a carbanion fulfills the criteria for being both a base and a nucleophile. Hence, the correct answer is (C) - (A) व (B) दोनों.