To solve this problem, we need to determine the nature of each oxide given in the question.$\\$Let's analyze each oxide:$\\$• $$CO (Carbon monoxide):$\\$CO is a neutral oxide. It does not react with acids or bases to form salts.$\\$• $$BaO (Barium oxide):$\\$BaO is a basic oxide. It reacts with water to form barium hydroxide, a strong base.$\\$• $$Al$_2$O$_3$ (Aluminum oxide):$\\$Al$_2$O$_3$ is an amphoteric oxide. It can react with both acids and bases.$\\$• $$Cl$_2$O$_7$ (Dichlorine heptoxide):$\\$Cl$_2$O$_7$ is an acidic oxide. It reacts with water to form perchloric acid.$\\$Now, let's match each oxide with its nature:$\\$(a) CO $\rightarrow$ (ii) Neutral$\\$(b) BaO $\rightarrow$ (i) Basic$\\$(c) Al$_2$O$_3 \rightarrow$ (iv) Amphoteric$\\$(d) Cl$_2$O$_7 \rightarrow$ (iii) Acidic$\\$Therefore, the correct option is:$\\$Option 1: (a) $\rightarrow$ (ii), (b) $\rightarrow$ (i), (c) $\rightarrow$ (iv), (d) $\rightarrow$ (iii)$\\$This corresponds to Option 1.