What is an adsorption isotherm? Describe Freundlich adsorption isotherm.

Explanation

### Step-by-Step Solution

**Step 1: Define Adsorption Isotherm**
An adsorption isotherm is a graphical representation that shows the relationship between the amount of gas adsorbed per gram of adsorbent (denoted as \( \frac{X}{M} \)) and the pressure of the gas at a constant temperature.

**Step 2: Explain the Variables**
- \( X \): Amount of gas adsorbed (in grams).
- \( M \): Mass of the adsorbent (in grams).
...