We know that propane is represented by the chemical formula: [tex] C_{3} H_{8} [/tex]
So the molar ratio of carbon to hydrogen is 3:8.
If we are given 0.2 moles of carbon, we can setup a proportion and solve for the number of moles of hydrogen present:
[tex] \frac{3}{8} =\frac{0.2}{x} [/tex]
Cross multiply and solve for x (moles of H):
[tex] 3x=1.6 [/tex]
[tex] x=0.53mol_{H} [/tex]
So now we know that when we are given 0.2 moles of carbon in propane, we get a respective 0.53 moles of hydrogen that are present.