Using the concept of oxidation number, identify the substances undergoing oxidaton and reduction in the following reactions.
`Zn+2HCl toZnCl_(2)+H_(2)`

Answer

To identify the substances undergoing oxidation and reduction in the reaction \( \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \) using the concept of oxidation numbers, we will follow these steps:

### Step 1: Assign Oxidation Numbers
- **Zinc (Zn)** in its elemental form has an oxidation number of **0**.
- In **HCl**, hydrogen (H) has an oxidation number of **+1** and chlorine (Cl) has an oxidation number of **-1**.
- In the product **ZnCl2**, zinc (Zn) has an oxidation number of **+2** and chlorine (Cl) remains at **-1**.
- In the product **H2**, hydrogen (H) in its elemental form has an oxidation number of **0**.

### Step 2: Write Down the Oxidation Numbers
- Reactants:
- Zn: 0
- H: +1 (in HCl)
- Cl: -1 (in HCl)

- Products:
- Zn: +2 (in ZnCl2)
- H: 0 (in H2)
- Cl: -1 (in ZnCl2)

### Step 3: Determine Changes in Oxidation Numbers
- **Zinc (Zn)**: Changes from **0** to **+2** (oxidation).
- **Hydrogen (H)**: Changes from **+1** to **0** (reduction).
- **Chlorine (Cl)**: No change in oxidation number (remains at **-1**).

### Step 4: Identify Oxidation and Reduction
- **Oxidation**: The process where a substance loses electrons, resulting in an increase in oxidation number. Here, zinc (Zn) is oxidized from 0 to +2.
- **Reduction**: The process where a substance gains electrons, resulting in a decrease in oxidation number. Here, hydrogen (H) is reduced from +1 to 0.

### Conclusion
- The substance undergoing **oxidation** is **Zinc (Zn)**.
- The substance undergoing **reduction** is **Hydrogen (H)**.

### Summary
- **Oxidation**: Zinc (Zn) → Oxidation number increases from 0 to +2.
- **Reduction**: Hydrogen (H) → Oxidation number decreases from +1 to 0.