Step 1: Understanding the Concept
Aldehydes and ketones react with ammonia derivatives \(\text{NH}_2-\text{Z}\) to form compounds with C=N-Z.
Step 2: Identify Z
For a semicarbazone, \(Z=-\text{NH}-\text{CO}-\text{NH}_2\), so the reagent is semicarbazide \(\text{NH}_2\text{NHCONH}_2\).
Step 3: Compare the options
(A) gives an oxime, (C) gives a phenylhydrazone and (D) gives a hydrazone. So (B) is correct.
Final Answer:
The reagent is semicarbazide.
\[ \boxed{\text{(B) }\text{NH}_{2}-\text{NH}-\text{CONH}_{2}} \]