what substance is being reduced in the following redox reaction?

HgCl2 + Sn^2 = Sn^4 + Hg2Cl2 + Cl-

To determine the substance being reduced in a redox reaction, we need to compare the oxidation states of the elements before and after the reaction. Here's how you can do it:

1. Identify the oxidation states of each element in the reaction.

In this redox reaction:

HgCl2 + Sn^2 = Sn^4 + Hg2Cl2 + Cl-

The oxidation states are as follows:
- For Hg (mercury), the oxidation state is +II in HgCl2 and is not changing in Hg2Cl2.
- For Cl (chlorine), the oxidation state is -I in HgCl2 and is not changing in Cl-.
- For Sn (tin), the oxidation state is +II in Sn^2 and is changing to +IV in Sn^4.

2. Determine which element is changing its oxidation state.

In this reaction, tin (Sn) is changing its oxidation state from +II to +IV.

3. The substance that is being reduced is the one that gains electrons or decreases its oxidation state.

Since tin (Sn) is changing from a lower oxidation state (+II) to a higher oxidation state (+IV), it is losing electrons and being oxidized, not reduced.

Therefore, the substance being reduced in this reaction is not present in the given equation.