Free Radical Chlorination of Methane to Tetrachloromethane

Steps:

• Methane (CH₄) undergoes stepwise free radical substitution with Cl₂ in sunlight.
• First step: CH₄ + Cl₂ → CH₃Cl + HCl (1 mole HCl).
• Second step: CH₃Cl + Cl₂ → CH₂Cl₂ + HCl (total 2 moles HCl).
• Third step: CH₂Cl₂ + Cl₂ → CHCl₃ + HCl (total 3 moles HCl).
• Fourth step: CHCl₃ + Cl₂ → CCl₄ + HCl (total 4 moles HCl from excess Cl₂).

Why D is correct:

• The overall balanced equation CH₄ + 4Cl₂ → CCl₄ + 4HCl shows 4 moles of HCl per mole of CH₄ in complete substitution.

Why the others are wrong:

• A: Represents only the monochlorination step.
• B: Represents substitution up to dichloromethane.
• C: Represents substitution up to trichloromethane.

Final answer: D