Question

KF has a NaCl structure. What is the distance (in pm) between $K^{+}$ and $F^{-}$ in KF if the density is $2.48$ g cm${}^{-3}$ $?

• A. $220$
• B. $135$
• C. $540$
• D. $269$

Answer 1

Answer: (D)

$269$

As we know,
for such structure
$2r^{+}+2r^{-}=a$
Also, as we know,
density $=nM/V{N}_o$
here, n= 4
$2.48=4\ast 58/\left(a{)}^3\right(N_o)$
distance between $K^{+}and{F}^{-}$ in KF = a/2 = 269 pm