Find the number of reaction from the given reaction which can show calcination process :
(i) `CaCO_(3).MgCO_(3) overset (Delta) rarr CaO + MgO + 2CO_(2)`
(ii) `CuCO_(3).Cu(OH)_(2) overset (Delta) rarr 2CuO + H_(2)O + CO_(2)`
(iii) `Al_(2)O_(3). 2H_(2)O overset (Delta) rarr Al_(2)O_(3) + 2H_(2)O`
(iv) `2Cu_(2)S + 3O_(2) overset (Delta) rarr 2Cu_(2) O + 2SO_(2)`.

Explanation

To determine the number of reactions that can show the calcination process from the given reactions, we need to understand what calcination is. Calcination is the process of heating an ore in limited or no supply of oxygen to convert it into its oxide. The temperature used in calcination is below the melting point of the ore.

Let's analyze each reaction step by step:

1. **Reaction (i)**:
\[ \text{CaCO}_3 + \text{MgCO}_3 \overset{\Delta}{\rightarrow} \text{CaO} + \text{MgO} + 2\text{CO}_2 \]
- In this reaction, calcium carbonate and magnesium carbonate are heated to produce their respective oxides and carbon dioxide. Since this reaction does not involve oxygen and is a thermal decomposition, it qualifies as calcination.

2. **Reaction (ii)**:
\[ \text{CuCO}_3 + \text{Cu(OH)}_2 \overset{\Delta}{\rightarrow} 2\text{CuO} + \text{H}_2\text{O} + \text{CO}_2 \]
- Here, copper carbonate and copper hydroxide are heated to form copper oxide, water, and carbon dioxide. This reaction also occurs without the presence of oxygen, making it another example of calcination.

3. **Reaction (iii)**:
\[ \text{Al}_2\text{O}_3 \cdot 2\text{H}_2\text{O} \overset{\Delta}{\rightarrow} \text{Al}_2\text{O}_3 + 2\text{H}_2\text{O} \]
- This reaction involves the dehydration of aluminum hydroxide to form aluminum oxide and water. Since it does not involve the conversion of an ore to its oxide in the presence of oxygen, it can also be considered as calcination.

4. **Reaction (iv)**:
\[ 2\text{Cu}_2\text{S} + 3\text{O}_2 \overset{\Delta}{\rightarrow} 2\text{Cu}_2\text{O} + 2\text{SO}_2 \]
- In this reaction, copper(I) sulfide is heated in the presence of oxygen to form copper(I) oxide and sulfur dioxide. Since this process requires oxygen, it is an example of roasting, not calcination.

Now, we can summarize the findings:

- Reactions that show calcination: (i), (ii), and (iii).
- Reaction that does not show calcination: (iv).

**Final Answer**: The number of reactions that involve calcination is **3**.