A binary solid (A B) has a rock salt structure. If the edge length is 400 pm and radius of cation is — Solid State Chemistry Question

💡 Solution & Explanation

In a rock salt (NaCl) structure, the edge length $a = 2(r_+ + r_-)$. Given $a = 400$ pm and $r_+ = 75$ pm, we have $400 = 2(75 + r_-)$. Solving gives $200 = 75 + r_-$, so $r_- = 125$ pm. Therefore, correct answer is B.