Thyroxine, an Important Hormone That Controls the Rate of Metabolism

Multiple Choice

Thyroxine, an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. If 0.455 g of thyroxine is dissolved in 10.0 g of benzene, the freezing point of the solution is 5.144°C. Pure benzene freezes at 5.444°C and has a value for the molal freezing-point-depression constant of K_f of 5.12°C/m. What is the molar mass of thyroxine?

A) 2330 g/mol
B) 285 g/mol
C) 777 g/mol
D) 3760 g/mol
E) 777,000 g/mol