A hydrocarbon contains 85.7% carbon and 14.3% hydrogen by mass and has a molar mass of 56 $g mo l^{- 1}$ . Its molecular formula is ( $C = 12$ , $H = 1$ )

Answer: B

Moles in 100 g: C = 85.7/12 = 7.14, H = 14.3/1 = 14.3; ratio H:C = 2.00, so the empirical formula is

CH X_{2}

(mass 14). 56/14 = 4, so the molecular formula is

C X_{4} H X_{8}

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