Primary products of butane cracking are C2 hydrocarbons Steps:

• Identify C4H10 as butane, an alkane cracked by breaking C-C bonds into smaller alkanes and alkenes.
• Note typical thermal cracking yields mainly C2 products via symmetric cleavage: C4H10 → C2H4 + C2H6.
• Consider asymmetric cleavage yields C1 + C3 fragments, where C3 radical forms C3H8 via H abstraction more readily than C3H6 via beta-elimination.
• Conclude C3H6 formation involves extra dehydrogenation step on C3 fragment, making it least favored.

Why D is correct:

• C3H6 (propene) requires specific beta-scission and H loss on the larger C3 radical, per free radical mechanism, less likely than C2 alkene formation.

Why the others are wrong:

• A: C2H6 forms directly in balanced equation C4H10 → C2H4 + C2H6.
• B: C2H4 forms directly in balanced equation C4H10 → C2H4 + C2H6.
• C: C3H8 forms via asymmetric break and H abstraction from C3 radical + CH3 to CH4.

Final answer: D