Question

A binary solid (AB) has a rock salt structure. If the edge length is 500 pm, and radius of a cation is 80 pm. Find the radius of an anion.

• A. 100 pm
• B. 120 pm
• C. 250 pm
• D. 170 pm

Answer 1

The correct option is D 170 pm

In Rock salt structure (NaCl) the relationship between $r^{+}$ ( radius of cation) , $r^{-}$ ( radius of anion) & 'a' ( edge length is ) :

$r^{+}$ + $r^{-}$ = a / 2

80 + $r^{-}$ = 500 / 2

$r^{-}$ = 170 pm .

Correct option is D