Pepsinogen is an inactive enzyme released by the gastric gland of stomach.
How is it activated?

Explanation

### Step-by-Step Solution:

1. **Understanding Pepsinogen**: Pepsinogen is a proenzyme (inactive form) secreted by the gastric glands in the stomach. It is important to note that it is not active until it undergoes a specific activation process.

2. **Role of Hydrochloric Acid (HCl)**: In the stomach, the gastric glands also secrete hydrochloric acid (HCl). This acid creates an acidic environment which is crucial for the activation of pepsinogen.

3. **Activation Process**: When pepsinogen comes into contact with hydrochloric acid, the acidic conditions lead to the release of hydrogen ions (H⁺). These hydrogen ions trigger a conformational change in the structure of pepsinogen.

...