Alkanes undergo free radical substitution reactions

Steps:

• Identify alkanes as saturated hydrocarbons with only single C-C and C-H bonds, lacking reactive pi bonds.
• Recognize that single bonds make addition reactions unlikely, favoring substitution where hydrogen atoms are replaced.
• Recall that alkanes react with halogens (e.g., Cl2) under UV light via a free radical chain mechanism.
• Confirm the mechanism involves initiation, propagation, and termination steps, leading to substitution products like alkyl halides.

Why B is correct:

• Free radical substitution matches alkanes' reactivity, as the homolytic cleavage of strong C-H bonds requires radicals, per the reaction CH4 + Cl2 → CH3Cl + HCl.

Why the others are wrong:

• A: Electrophilic addition targets pi bonds in unsaturated compounds like alkenes, absent in alkanes.
• C: Electrophilic substitution occurs on aromatic rings to preserve stability, not on saturated alkanes.
• D: Nucleophilic addition involves electron-rich species attacking partial positives, irrelevant to non-polar alkanes.

Final answer: B