Which of the following expressions is correct in case of a CsCl unit cell (edge length 'a')?

Options

A. `r_(Cs^+) + r_(Cl^-) = a/sqrt2`
B. `r_(Cs^+) + r_(Cl^-) = a/2`
C. `r_(Cs^+) + r_(Cl^-) = a`
D. `r_(Cs^+) + r_(Cl^-) = sqrt3/2a`