The correct answer is A) Water.
SN2 reactions (substitution nucleophilic bimolecular) involve a nucleophile attacking a substrate, resulting in a simultaneous bond-breaking and bond-forming process. In SN2 reactions, a good leaving group and a strong nucleophile are required.
Among the given options, water (option A) is a polar solvent and is known to favor SN2 reactions. Water can solvate both the nucleophile and the substrate due to its polarity, facilitating their interaction and increasing the reaction rate.
Ammonia (option B) is also a polar solvent and can favor SN2 reactions to some extent, but it is generally not as effective as water in promoting these reactions.
Carbon tetrachloride (option C) is a nonpolar solvent and is not suitable for SN2 reactions as it lacks the ability to solvate and stabilize the nucleophile and the substrate.
Acetic acid (option D) is a polar solvent, but it can hinder SN2 reactions due to its ability to protonate the nucleophile and decrease its reactivity.
Therefore, among the given options, water (option A) is the solvent that favors SN2 reactions the most.
I hope this helps.