**Core Concept**
Arsenic poisoning interferes with the normal metabolic processes of bacteria involved in putrefaction, particularly by inhibiting bacterial enzymes responsible for protein degradation. This leads to delayed decomposition of tissues post-mortem.

**Why the Correct Answer is Right**
Arsenic acts as a potent inhibitor of bacterial enzymes such as those in the urease and proteolytic pathways, which are essential for putrefaction. It disrupts microbial activity in the body, thereby retarding the breakdown of tissues. This is a well-documented forensic hallmark of arsenic poisoning, making it a key indicator in post-mortem investigations.

**Why Each Wrong Option is Incorrect**
Option A: Aluminium phosphide causes rapid decomposition due to phosphine gas release, accelerating putrefaction, not retarding it.
Option B: Lead poisoning may cause tissue damage but does not specifically inhibit bacterial degradation; it does not delay putrefaction.
Option D: Copper is a trace element with minimal effect on putrefaction; it does not significantly alter microbial metabolism in the body.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, arsenic poisoning is clinically recognized by delayed putrefaction — a key feature that helps differentiate it from other toxicities. Always remember: *Arsenic slows putrefaction; other poisons may accelerate it.*

✓ Correct Answer: C. Arsenic