A solid substance AB has a rock salt geometry. What is the coordination number of A and B ? Ho amy atoms oif A and B are presnet in the unit cell ?

Explanation

To solve the problem, we need to analyze the rock salt structure, which is a common crystal structure for ionic compounds like sodium chloride (NaCl) and is characterized by a face-centered cubic (FCC) lattice.

### Step 1: Understanding the Rock Salt Structure
In a rock salt structure, the cations (A) and anions (B) are arranged in a specific manner. The cations occupy the octahedral holes of the face-centered cubic lattice formed by the anions.

### Step 2: Coordination Number
1. **Coordination Number of A**: In the rock salt structure, each cation (A) is surrounded by six anions (B). Therefore, the coordination number of A is 6.
2. **Coordination Number of B**: Similarly, each anion (B) is surrounded by six cations (A). Thus, the coordination number of B is also 6.
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