To solve this problem, we need to match the chemical reactions in List I with their corresponding environmental effects in List II. Let's analyze each reaction and its environmental impact:$\newline 1. Reaction (a): ( 2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)) \newline -$This reaction involves the conversion of sulfur dioxide (SO$_2$) to sulfur trioxide (SO$_3$).$-$Sulfur trioxide can react with water to form sulfuric acid, contributing to acid rain.$-$Therefore, this reaction is associated with acid rain.$\newline 2. Reaction (b): (HOCl (g) \xrightarrow{h\nu} \overset{\cdot}{O}H + \overset{\cdot}{C}) \newline -$This reaction involves the photodissociation of hypochlorous acid (HOCl) into hydroxyl radicals and chlorine radicals.$-$Chlorine radicals are known to deplete ozone in the stratosphere.$-$Therefore, this reaction is associated with ozone depletion.$\newline 3. Reaction (c): ({CaCO}_3 + {H}_2{SO}_4 \rightarrow {CaSO}_4 + {CO}_2 + {H}_2{O}) \newline -$This reaction describes the reaction of calcium carbonate with sulfuric acid, producing calcium sulfate, carbon dioxide, and water.$-$This is a typical reaction that occurs in the presence of acid rain, which affects limestone and marble structures.$-$Therefore, this reaction is associated with acid rain.$\newline 4. Reaction (d): ({NO}_2(g) \xrightarrow{h\nu} {NO}(g) + {O}(g)) \newline -$This reaction involves the photodissociation of nitrogen dioxide (NO$_2$) into nitric oxide (NO) and atomic oxygen.$-$This reaction is a part of the photochemical smog formation process.$-$Therefore, this reaction is associated with smog.$\newline$Based on the analysis, we can match the reactions with their effects:$- (a) \rightarrow (i)$Acid rain$- (b) \rightarrow (iii)$Ozone depletion$- (c) \rightarrow (i)$Acid rain$- (d) \rightarrow (ii)$Smog$\newline$Thus, the correct option is: $\newline$Option 3:$(a) \rightarrow (i), (b) \rightarrow (iii), (c) \rightarrow (i), (d) \rightarrow (ii)$