Science (086) — AI-generated practice question

The student is not correct. Not every combination reaction is exothermic.

A combination reaction simply involves two or more substances combining to form a single product. While many combination reactions do release heat — for example:

$$\text{CaO}(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(aq) + \text{Heat}$$

— this is not a defining feature of all combination reactions.

The formation of water ($2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$) and burning of coal ($\text{C} + \text{O}_2 \rightarrow \text{CO}_2$) are also exothermic combination reactions, but there exist combination reactions that require energy input (endothermic). Exothermic nature is a property of some combination reactions, not all.

Source: Chapter 1, Section 1.2.1 Combination Reaction

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• CBSE expects you to clearly state the student is wrong, then justify with a definition of combination reaction and at least one example.
• The key distinction: combination reaction is defined by structure (many → one), not by energy change. Exothermic reactions are separately defined as those releasing heat.
• Mention both the definition and at least one example reaction with equation for full 3-mark credit.
• Avoid writing a long essay — the answer above is appropriately concise for 3 marks.