Final answer:
The percent by mass of carbon in hydrocortisone valerate is 77.56%.
Step-by-step explanation:
To find the percent by mass of carbon in hydrocortisone valerate, we need to calculate its molar mass and the mass of carbon in the compound. The molar mass of hydrocortisone valerate (C26H38O6) can be determined by summing the masses of each element. Carbon has a molar mass of 12.01 g/mol, hydrogen has a molar mass of 1.01 g/mol, and oxygen has a molar mass of 16.00 g/mol.
So, the molar mass of hydrocortisone valerate is (26*12.01)+(38*1.01)+(6*16.00) = 402.38 g/mol. Next, we find the mass of carbon in the compound by multiplying the number of carbon atoms (26) by the molar mass of carbon (12.01 g/mol). The mass of carbon in hydrocortisone valerate is (26*12.01) = 312.26 g. Finally, we calculate the percent by mass of carbon by dividing the mass of carbon by the molar mass of the compound and multiplying by 100%. The percent by mass of carbon in hydrocortisone valerate is (312.26/402.38) * 100% = 77.56%. Rounded to two decimal places, it is approximately 77.56%. Therefore, the answer is not listed among the options provided.