Ammonium chloride on heating gives `NH_3 and HCI`,which on cooling again form ammonium chloride. This reaction is called

Options

A. lonic dissociation
B. thermal decomposition
C. thermal dissociation
D. double decomposition

Explanation

To solve the question regarding the reaction of ammonium chloride when heated, we can break down the process step by step:

### Step 1: Identify the Reaction
When ammonium chloride (NH4Cl) is heated, it decomposes into ammonia (NH3) and hydrochloric acid (HCl). This can be represented by the following chemical equation:
\[ \text{NH}_4\text{Cl (s)} \rightarrow \text{NH}_3\text{ (g)} + \text{HCl (g)} \]

### Step 2: Understand the Process
This reaction involves the breakdown of a single compound (ammonium chloride) into two simpler substances (ammonia and hydrochloric acid) due to the application of heat. This type of reaction is characterized by the breaking down of a compound into its components.

### Step 3: Cooling and Reformation
Upon cooling, ammonia and hydrochloric acid can recombine to form ammonium chloride again:
\[ \text{NH}_3\text{ (g)} + \text{HCl (g)} \rightarrow \text{NH}_4\text{Cl (s)} \]

### Step 4: Classify the Reaction
This entire process can be classified under a specific type of reaction. Given the options provided:
- **Ionic Dissociation** refers to the breaking down of ionic compounds into ions, typically in solution.
- **Thermal Decomposition** is the process where a compound breaks down into simpler substances due to heat.
- **Thermal Dissociation** is similar to thermal decomposition but emphasizes the breakdown due to heat.
- **Double Decomposition** involves two compounds reacting to form two new compounds.

In this case, since ammonium chloride is breaking down into ammonia and hydrochloric acid due to heat, the correct classification of this reaction is **Thermal Decomposition**.

### Final Answer
The reaction of ammonium chloride on heating, which produces ammonia and hydrochloric acid and can reform upon cooling, is called **Thermal Decomposition**.

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