(A) Phenol, Zn/$\Delta$: When phenol is treated with zinc dust and heated, it gets reduced to benzene. Thus, (A) corresponds to (III) Benzene.
(B) Phenol, CHCl$_3$, NaOH, HCl (Reimer-Tiemann Reaction): Phenol undergoes the Reimer-Tiemann reaction with chloroform and aqueous sodium hydroxide, forming salicylaldehyde. Thus, (B) corresponds to (I) Salicylaldehyde.
(C) Phenol, CO$_2$, NaOH, HCl (Kolbe-Schmitt Reaction): Phenol reacts with carbon dioxide under high pressure in the presence of sodium hydroxide, followed by acidification, to form salicylic acid. Thus, (C) corresponds to (II) Salicylic acid.
(D) Phenol, Conc. HNO$_3$: Phenol reacts with concentrated nitric acid to form picric acid (2,4,6-trinitrophenol). Thus, (D) corresponds to (IV) Picric acid.
Conclusion: The correct matching is (A)-(III), (B)-(I), (C)-(II), (D)-(IV).
A body of mass 1000 kg is moving horizontally with a velocity of 6 m/s. If 200 kg extra mass is added, the final velocity (in m/s) is: