In basic chemistry, which of the following reactions are correctly classified as exothermic processes, that is, reactions that release heat energy to the surroundings?

Introduction / Context:
Exothermic reactions are chemical changes in which energy is released to the surroundings, usually in the form of heat or sometimes light. In introductory chemistry, students often see examples such as combustion, formation of ionic compounds from metals and nonmetals, and hydration of certain salts. This question asks you to judge whether three specific reactions are exothermic and to recognise that more than one of them can release heat. Understanding which typical textbook reactions are exothermic helps in predicting temperature changes during experiments and in everyday processes such as burning fuels or setting plaster.

Given Data / Assumptions:

• Reaction 1: C + O2 → CO2
• Reaction 2: 2Mg + O2 → 2MgO
• Reaction 3: CuSO4 + 5H2O → CuSO4·5H2O
• All reactions are considered under normal laboratory conditions.
• Exothermic means overall release of heat to the surroundings.

Concept / Approach:
The concept is that exothermic reactions have a negative enthalpy change because products have lower chemical energy than reactants. Combustion of elements like carbon and magnesium are classic exothermic processes. Hydration of anhydrous copper sulfate to the blue pentahydrate is also exothermic, which is why the solid heats up when water is added. The approach is to recall standard examples of exothermic reactions from basic chemistry and match them to the listed reactions, rather than trying to calculate enthalpy values numerically.

Step-by-Step Solution:
Step 1: Consider reaction 1, C + O2 → CO2. Combustion of carbon in oxygen to form carbon dioxide is a classic exothermic reaction; it releases heat and sometimes visible light as a flame. Step 2: Consider reaction 2, 2Mg + O2 → 2MgO. Burning magnesium ribbon in air produces a bright white flame and releases a lot of heat, again making this a clear exothermic reaction. Step 3: Consider reaction 3, CuSO4 + 5H2O → CuSO4·5H2O. When water is added to white anhydrous copper sulfate, it becomes blue hydrated copper sulfate and the process releases heat, so this hydration is also exothermic. Step 4: Since all three reactions individually are exothermic, the correct classification is that reactions 1, 2 and 3 are all exothermic.

Verification / Alternative check:
Another way to check is from experimental observations. When carbon or magnesium burn, the surroundings definitely become hotter, which is a direct sign of heat release. With anhydrous copper sulfate, a noticeable temperature rise is felt if you carefully touch the container after adding water. Many data tables in chemistry textbooks and handbooks also list negative enthalpy changes for combustion reactions and hydration of copper sulfate, confirming their exothermic nature. These independent references support the conclusion that each of the three reactions releases heat overall.

Why Other Options Are Wrong:
Option A is wrong because it ignores the obviously exothermic combustion of magnesium and the exothermic hydration of copper sulfate. Option B fails to recognise that reaction 3 is also exothermic. Option C incorrectly leaves out reaction 1, which is one of the most famous exothermic processes. Option D wrongly suggests that only two of the three are exothermic. Only option E correctly states that all three listed reactions are exothermic.

Common Pitfalls:
A common mistake is to assume that only burning reactions are exothermic and to forget that hydration or neutralisation processes can also release heat. Some learners also think that any reaction involving water must be endothermic, which is not always true. It is important to rely on known examples and experimental evidence rather than guessing from appearance alone. Another pitfall is confusing exothermic with fast or dramatic reactions, but some exothermic changes can be slow or gentle while still releasing heat overall.

Final Answer:
The correct choice is All three reactions 1, 2 and 3 are exothermic because each one releases heat to the surroundings when it occurs under normal conditions.