Step 1: Identify the reactions.
- (a) \( \text{[Ag(NH}_3)_2]^+ \) is used in the Tollens reagent, which is used for the detection of aldehydes.
- (b) \( \text{Zn-Hg}/\text{HCl} \) is used in the Clemmenesen reduction for converting carbonyl compounds to alkanes.
- (c) \( \text{NH}_2 - \text{NH}_2/\text{KOH} \) is used in the Wolff-Kishner reduction for reducing aldehydes or ketones to alkanes.
- (d) \( \text{Cu}^{2+}/\text{OH}^- \) is used in Fehling's solution for the detection of reducing sugars.
Step 2: Conclusion.
Thus, the correct match is:
\[
\text{a(iii), b(ii), c(iv), d(i)}
\]
Final Answer:
\[
\boxed{\text{a(iii), b(ii), c(iv), d(i)}}
\]