Reactants:
- Alkyl halide
- Alcoholic/ammoniacal ammonia

Explanation:
The reaction of alkyl halides with alcoholic/ammoniacal ammonia is a nucleophilic substitution reaction in which the nucleophile attacks the carbon atom of the alkyl halide, replacing the halogen atom. The nucleophile in this reaction can be identified by its ability to donate a pair of electrons to form a new covalent bond with the carbon atom.

Possible Nucleophiles:
A. H
B. NO2^-
C. Br^-
D. NH3

Analysis:
In this reaction, the alkyl halide reacts with either alcoholic or aqueous ammonia, both of which contain a nucleophile. Let's analyze each option to determine which one acts as the nucleophile in this reaction.

A. H:
- Hydrogen (H) is not a nucleophile as it does not possess a lone pair of electrons.
- Hydrogen ion (H+) can act as an acid, but not as a nucleophile in this reaction.

B. NO2^-:
- Nitrite ion (NO2^-) is a poor nucleophile as it is electron-withdrawing due to the presence of the electronegative oxygen atom.
- It can act as a leaving group, but not as a nucleophile in this reaction.

C. Br^-:
- Bromide ion (Br^-) is a good nucleophile as it is electron-rich and has a lone pair of electrons.
- It can readily attack the carbon atom of the alkyl halide, displacing the halogen atom.
- Therefore, Br^- acts as a nucleophile in this reaction.

D. NH3:
- Ammonia (NH3) is a weak nucleophile as it has a lone pair of electrons but less electron density compared to Br^-.
- It can still act as a nucleophile and participate in the reaction, but its nucleophilic strength is lower compared to Br^-.
- Therefore, NH3 acts as a nucleophile, but less efficiently than Br^-.

Conclusion:
In the reaction of alkyl halide with alcoholic/ammoniacal ammonia, the nucleophile is Br^- (bromide ion) followed by NH3 (ammonia). Br^- is the strongest nucleophile among the options provided.