A mixture of methane ( $CH X_{4}$ ) and ethane ( $C X_{2} H X_{6}$ ) occupies $5.6 L$ at STP and has a mass of $5.4 g$ (C = 12, H = 1; molar volume $22.4 L mo l^{- 1}$ ). The number of hydrogen atoms in the mixture, in units of $N_{A}$ , is:

Answer: C

Total moles

= 5.6/22.4 = 0.25

. Let ethane be

y

16 (0.25 - y) + 30 y = 5.4

, so

y = 0.10

and methane

= 0.15

mol. H atoms

= 4 (0.15) + 6 (0.10) = 1.2 N_{A}