• Chemical Mutagens and Mechanisms of Mutagenesis:
• Pair-by-Pair Matching:
• Nitrous acid $\rightarrow$ (IV) $\text{AT} \rightarrow \text{GC}$ and $\text{GC} \rightarrow \text{AT}$: Deaminates adenine to hypoxanthine (pairs with C, causing $\text{AT} \rightarrow \text{GC}$) and cytosine to uracil (pairs with A, causing $\text{GC} \rightarrow \text{AT}$).
• 2-aminopurine (2-AP) $\rightarrow$ (V) $\text{AT} \rightarrow \text{GC}$ and occasionally $\text{GC} \rightarrow \text{AT}$: A purine base analog that normally pairs with thymine but frequently mispairs with cytosine, inducing primarily $\text{AT} \rightarrow \text{GC}$ transitions.
• Nitrosoguanidine (MNNG) $\rightarrow$ (I) Both point mutation and deletion: A potent alkylating agent that methylates guanine ($O^6$-methylguanine) and induces extensive transitions along with cluster mutations and small deletions.
• Ethyl methanesulfonate (EMS) $\rightarrow$ (II) $\text{GC} \rightarrow \text{AT}$: Specifically ethylates guanine at the $O^6$ position ($O^6$-ethylguanine), which pairs with thymine during replication, causing targeted $\text{GC} \rightarrow \text{AT}$ transitions.
• Ethidium bromide $\rightarrow$ (III) Microinsertion and microdeletion: An intercalating planar fluorophore that slips between adjacent stacked base pairs, distorting the helix and causing single base insertions/deletions (frameshift mutations) during replication.
• Correct Choice: Option 4 matches (A)-(IV), (B)-(V), (C)-(I), (D)-(II), (E)-(III).

Correct option: (4) (A) (IV), (B) - (V), (C) - (1), (D) — (I), (E) — (I)