$word_{count}$: 220

Selecting the correct reducing agent is critical for JEE synthesis problems. NaBH4: gentle, reduces only aldehyde/ketone C=O → alcohol; safe in protic solvents; leaves COOH, COOR, CONR2, C=C, CN untouched. LiAlH4: aggressive, reduces virtually all C=O-containing groups (RCHO, R2CO, RCOOH, RCOOR', RCONR2, RCN, epoxides) → alcohols/amines; must use anhydrous ether/THF. DIBAL-H at -78°C: stops at aldehyde when starting from ester or nitrile — temperature-controlled selectivity. Rosenmund (H2/Pd-BaSO4 poisoned): acid chloride → aldehyde selectively. Stephen $\frac{SnCl2}{HCl}$: nitrile → aldehyde. Clemmensen (Zn-Hg/HCl): complete reduction C=O → CH2 in ACIDIC conditions — for acid-stable substrates. Wolff-Kishner $\frac{NH2NH2}{KOH}$: same transformation in BASIC conditions — for base-stable substrates. MPV (Al(OiPr)3): highly selective ketone → alcohol, leaving all other groups untouched. Catalytic H2/Pd: primarily reduces C=C > C=O. For alpha,beta-unsaturated carbonyls: NaBH4 → 1,2-reduction (allylic alcohol), R2CuLi → 1,4-reduction (saturated ketone), H2/Pd → saturated alcohol (both reduced). Choice depends on what other groups must survive.