Which of the following expressions is correct in the case of a sodium chloride unit cell (edge length, `a`)?

Options

A. `r_(c )+ r_(a) = a//2`
B. `r_(c ) + r_(a) = a`
C. `r_(c )+ r_(a) = 2a`
D. `r_(c ) r_(a) = 2^(1//2)a`

Answer

b

Explanation

`2(r_(c) + r_(a)) = a`