The `gamma`-form of iron has `fcc` structure (edge length `386 pm`) and `beta`-form has `bcc` structure (edge length `290 pm`). The ratio of density in `gamma`-form and `beta`-form is

Options

A. `0.9788`
B. `1.02`
C. `1.57`
D. `0.6344`

Answer

A

Explanation

`Z_(eff)` for fcc `= 4` and forbcc `= 2//"unit cell"`
`(rho_(lambda))/(rho_(beta))=(rho_(fc c))/(rho_(fc c))=(Z_(eff(fc c))/(Z_(eff(bc c))))xx((a_(bc c))/(a_(fc c)))^(3)`
`= 4/2 xx ((290)/(386))^(3) = 0.9788`