Chemistry

The key here is recognizing reduction of mercury — you need to identify which reagent can donate electrons to $\text{Hg}^{2+}$ and bring it down to metallic $\text{Hg}^0$. Think about what makes a good reducing agent: it should be easily oxidized itself. Common reducing agents in inorganic chemistry include metals (like Cu or Fe), hydrogen gas, or carbon-based reagents. The trick is finding one that's strong enough to reduce mercury but practical in a lab setting.

The key here is recognizing reduction of mercury — you need to identify which reagent can donate electrons to $\text{Hg}^{2+}$ and bring it down to metallic $\text{Hg}^0$. Think about what makes a good reducing agent: it should be easily oxidized itself. Common reducing agents in inorganic chemistry include metals (like Cu or Fe), hydrogen gas, or carbon-based reagents. The trick is finding one that's strong enough to reduce mercury but practical in a lab setting.