The major products obtained from the reactions in List-II are the reactants for the named reactions mentioned in List-I. Match List-I with List-II and choose the correct option.

The correct option is P → 3; Q → 4; R → 5; S → 2.

To match List-I (named reactions) with List-II (reactions yielding major products that serve as starting reactants), let us analyze the products formed in each reaction of List-II from the provided image:

Analysis of Reactions in List-II:

1. Acetophenone + Zn-Hg/HCl (Clemmensen Reduction):
Acetophenone (C₆H₅COCH₃) undergoes reduction to form ethylbenzene (C₆H₅CH₂CH₃).

2. Toluene + (i) KMnO₄, KOH, Δ (ii) SOCl₂:
First, oxidation of toluene yields benzoic acid (C₆H₅COOH). Subsequent treatment with thionyl chloride (SOCl₂) converts benzoic acid into benzoyl chloride (C₆H₅COCl).
Benzoyl chloride (C₆H₅COCl) is the starting reactant for the Rosenmund reduction (S → 2).

3. Benzene + CH₃Cl / anhyd. AlCl₃ (Friedel-Crafts Alkylation):
Reaction of benzene with methyl chloride in the presence of anhydrous AlCl₃ forms toluene (C₆H₅CH₃).
Toluene is the starting reactant for the Etard reaction, which oxidizes toluene to benzaldehyde using chromyl chloride (P → 3).

4. Aniline + NaNO₂ / HCl at 273-278 K (Diazotization):
Diazotization of aniline yields benzene diazonium chloride (C₆H₅N₂⁺Cl^-).
Benzene diazonium chloride reacts with Cu/HCl or Cu/HBr to form haloarenes, which is known as the Gattermann reaction (Q → 4).

5. Phenol + Zn, Δ (Reduction):
Heating phenol with zinc dust yields benzene (C₆H₅).
Benzene is treated with CO and HCl in the presence of anhydrous AlCl₃/CuCl to form benzaldehyde, which is known as the Gattermann-Koch reaction (R → 5).

Summary of Matching:

(P) Etard reaction → (3) Toluene (obtained from Benzene + CH₃Cl / anhyd. AlCl₃)
(Q) Gattermann reaction → (4) Benzene diazonium chloride (obtained from Aniline + NaNO₂/HCl)
(R) Gattermann-Koch reaction → (5) Benzene (obtained from Phenol + Zn, Δ)
(S) Rosenmund reduction → (2) Benzoyl chloride (obtained from Toluene + KMnO₄ then SOCl₂)

Thus, the correct matching combination is P → 3; Q → 4; R → 5; S → 2.