LIST - 1 (Conversion)	LIST - 2  (Process involved)
A) Benzene Cyclohexane	1) Hydration reaction
B) Ethylene → Formaldehyde	2) Controlled hydrogenation
C) Acetylene → Ethylene	3) Hydrogenation reaction
D) Benzene → Toluene	4) Ozonolysis
	5) Alkylation

Hydration reaction: In this water is added to unsaturated substrates.
Controlled hydrogenation: In presences of (${\mathrm{H}}_2~\mathrm{Pd}$/BaSO₄) alkynes converted into alkenes.
Hydrogenation reaction: In this process unsaturated compounds completely converted into saturated compounds in presence of (${\mathrm{H}}_2$/Ni).
Ozonolysis: cleavage of the unsaturated double bond in presence of ozone and the addition of an oxygen atom to each.
Alkylation: it is done in the presences of catalyst ${\mathrm{AlCl}}_3$ when benzene is reacted with ${\mathrm{CH}}_3\mathrm{Cl}$.
Therefore correct option is (C) A→3, B→4, C→2, D→5.