Propane has the formula c3h8. if a sample of propane contains 0.20 moles of c, how many moles of h are present?

Solving this problem only requires the knowledge of stoichiometry. We are given the compound propane C3H8. From the chemical formula, we can see that for every 3 moles of C, there are 8 moles of H. Therefore:

moles of H = 0.20 moles C * (8 moles H / 3 moles C)

moles of H = 0.53 moles H

that's what i got you can count the number of atoms

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.