A student investigated the displacement reactions between different metals and iron(II) sulfate solution.
The student measured 50 cm350\text{ cm}^350 cm3 of iron(II) sulfate solution into a polystyrene cup, recorded the starting temperature, added a metal, and measured the maximum temperature change.
Table 1 shows the student's results:
| Metal | Temperature change (∘C^{\circ}\text{C}∘C) |
|---|---|
| Magnesium | +25+25+25 |
| Zinc | +12+12+12 |
| Copper | 000 |
Identify the independent variable and the dependent variable in this investigation.
Write the three metals in order of decreasing reactivity (from most reactive to least reactive).
The reaction profile for the reaction between magnesium and iron(II) sulfate solution is shown below.

Which letter represents the activation energy, and which letter represents the products?