A substance has a face centred cubic crystal with a density `1.984` g `cm^(-3)` and edge length 630 pm. Calculate the molar mass of the substance

Options

A. `37.35 g mol^(-1)`
B. `56.02 g mol^(-1)`
C. `74.70 g mol^(-1)`
D. `65.36 g mol^(-1)`

Answer

C

Explanation

`M=( a^(3) rho ("Av. Number"))/("No. of atoms in unit cell")`
`=((630xx10^(-10) cm) ^(3)(1.984 g cm^(-3)) (6.023xx10^(23)"mol"^(-1)))/(4)`
`=74.7 g "mol"^(-1)`