Calcination and roasting are :

Options

A. different names of same operation
B. used for the purification of metals
C. usually carried in the reverberatory furnace
D. employed for the concentration of the ore.

Explanation

**Step-by-Step Solution:**

1. **Definition of Calcination:**
- Calcination is a thermal treatment process where an ore is heated in the absence of air. The primary purpose of this process is to convert the ore into its oxide form.

2. **Example of Calcination:**
- A common example of calcination is the heating of calcium carbonate (CaCO₃). When calcium carbonate is heated without air, it decomposes to form calcium oxide (CaO) and carbon dioxide (CO₂) gas:
\[ \text{CaCO}_3 \, (\text{s}) \xrightarrow{\text{heat}} \text{CaO} \, (\text{s}) + \text{CO}_2 \, (\text{g}) \]

3. **Another Example of Calcination:**
- Similarly, magnesium carbonate (MgCO₃) undergoes calcination when heated in the absence of air, resulting in magnesium oxide (MgO) and carbon dioxide (CO₂):
\[ \text{MgCO}_3 \, (\text{s}) \xrightarrow{\text{heat}} \text{MgO} \, (\text{s}) + \text{CO}_2 \, (\text{g}) \]

4. **Definition of Roasting:**
- Roasting is another thermal treatment process, but in this case, the ore is heated in the presence of air. The aim of roasting is also to convert the ore into its oxide form.

5. **Example of Roasting:**
- A typical example of roasting is the heating of lead sulfide (PbS) in the presence of air. When PbS is roasted, it converts into lead oxide (PbO) and sulfur dioxide (SO₂) gas:
\[ \text{2PbS} \, (\text{s}) + \text{3O}_2 \, (\text{g}) \xrightarrow{\text{heat}} 2\text{PbO} \, (\text{s}) + 2\text{SO}_2 \, (\text{g}) \]

6. **Comparison of Calcination and Roasting:**
- In summary, calcination occurs in the absence of air and typically involves carbonates, while roasting occurs in the presence of air and often involves sulfides.