Answer:
C
Step-by-step explanation:
Well, we can see from the equation that hydrogen gas and ethane are in a 2:1 ratio based on their mole coefficients.
You need 2 mol H2 to make 1 mol C2H6. So that means you need 2*13.78 mol H2 to make 13.78 mol C2H6!
2*13.78 = 27.56 mol
C is correct.