what is the percent by mass of carbon in c3h8?

I don't think so.

%Carbon = (3*atomic mass C/molar mass C3H8)*100 = ?

C. 81.8%

That's right. Now you do that other problem the same way.

To calculate the percent by mass of carbon in C3H8, we need to determine the molar mass of carbon in C3H8 and then divide it by the molar mass of the entire compound.

To find the molar mass of carbon (C), we take the atomic mass of carbon from the periodic table, which is approximately 12.01 g/mol.

Next, we calculate the molar mass of the entire compound C3H8.

The molar mass of carbon (C) is 12.01 g/mol, and there are three carbon atoms in C3H8, so the mass of carbon in the compound is 12.01 g/mol x 3 = 36.03 g/mol.

The molar mass of hydrogen (H) is approximately 1.01 g/mol, and there are eight hydrogen atoms in C3H8, so the mass of hydrogen in the compound is 1.01 g/mol x 8 = 8.08 g/mol.

To find the molar mass of C3H8, we add the molar masses of carbon and hydrogen: 36.03 g/mol + 8.08 g/mol = 44.11 g/mol.

Next, we determine the percent by mass of carbon in C3H8 by dividing the mass of carbon by the molar mass of the compound and multiplying by 100%.

(36.03 g/mol / 44.11 g/mol) x 100% = 81.72%

Therefore, the correct answer is C. 81.8%.