The answer to the question is (2) The standard reduction potential of iron is less than that of copper.
Here's why this is the correct answer:
- The standard reduction potential is a measure of a metal's tendency to gain electrons and be reduced from a cation to a metal atom in an electrochemical reaction. Metals with more negative reduction potentials are better reducing agents (more reactive) than metals with less negative or positive reduction potentials.
- In the reaction between iron and copper sulfate, iron ( $\mathrm{Fe}$ ) is displacing copper $(\mathrm{Cu})$ from its salt solution $\left(\mathrm{CuSO}_4\right)$. This means iron is more reactive than copper.
- Iron has a more negative standard reduction potential than copper, which means it is easier for iron to be reduced (gain electrons) than copper. This greater ease of reduction allows iron to take electrons away from the copper ions in copper sulfate, reducing the copper ions to copper metal and oxidizing itself to ferrous iron $\left(\mathrm{Fe}^{2+}\right)$.