Science (086) — AI-generated practice question

Although saturated hydrocarbons are generally inert to most reagents, they can still undergo substitution reactions under specific conditions. In this reaction, a chlorine atom replaces one hydrogen atom of methane to form chloromethane (CH₃Cl) and HCl.

Sunlight is essential because it provides the energy needed to activate the chlorine molecules (Cl₂), enabling the reaction to proceed. Without sunlight, the activation energy is not supplied, so the reaction does not occur. This is why the same mixture of methane and chlorine shows no reaction in the dark.

$$\text{CH}_4 + \text{Cl}_2 \xrightarrow{\text{sunlight}} \text{CH}_3\text{Cl} + \text{HCl}$$

Source: Chapter 4, Section 4.3.4 – Substitution Reaction

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• Examiners expect two clear points: (1) saturated hydrocarbons are inert under normal conditions but not absolutely unreactive, and (2) sunlight provides the activation energy needed to initiate the reaction.
• Name the reaction type (substitution reaction) — this is a key term the examiner will look for.
• Writing the balanced equation with the condition (sunlight) shown earns a mark on its own.
• Don't write about free radicals or chain mechanisms — that is beyond CBSE Class 10 scope and wastes word budget.