The structure of `MgO` is similar to NaCl. What is the co- ordination number of `Mg`?

Answer

To determine the coordination number of magnesium (Mg) in magnesium oxide (MgO), we can follow these steps:

### Step 1: Understand the Structure
The question states that the structure of MgO is similar to that of NaCl. Both of these compounds crystallize in a rock salt structure, which is a face-centered cubic (FCC) lattice.

**Hint:** Remember that in a rock salt structure, the cations and anions are arranged in a specific way that allows us to determine their coordination numbers.

### Step 2: Identify the Charges
In MgO, magnesium has a +2 charge (Mg²⁺) and oxygen has a -2 charge (O²⁻). This means that each Mg²⁺ ion will be surrounded by anions to maintain charge neutrality.

**Hint:** The charge of the ions can help you understand how they interact in the crystal lattice.

### Step 3: Analyze the Coordination Number
In the rock salt structure, each cation (Mg²⁺) is surrounded by anions (O²⁻) and vice versa. For a cation in an FCC lattice, the coordination number is determined by how many nearest neighbor anions surround it.

**Hint:** The coordination number is the number of nearest neighbors surrounding a central atom.

### Step 4: Determine the Coordination Number
In the case of MgO, each Mg²⁺ ion is surrounded by 6 O²⁻ ions. This is because in an octahedral arrangement, there are 6 points of contact around the central ion.

**Hint:** Visualizing the arrangement of ions can help you see how many ions surround the central ion.

### Step 5: Conclusion
Thus, the coordination number of magnesium (Mg) in MgO is **6**.

**Final Answer:** The coordination number of Mg in MgO is 6.

---