According to Langmuir adsorption isotherm, the amount of gas adsorbed at very high pressure:

Options

A. Reaches a constant limiting value
B. Goes on increasing with pressure
C. Goes on decreasing with pressrue
D. Increases first and decreases later with pressure

Answer

To solve the question regarding the Langmuir adsorption isotherm and the amount of gas adsorbed at very high pressure, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Langmuir Adsorption Isotherm Equation**:
The Langmuir adsorption isotherm is given by the equation:
\[ \frac{x}{m} = \frac{A p}{1 + A p} \]
where:
- \( x \) = amount of gas adsorbed
- \( m \) = mass of the adsorbent
- \( A \) = constant related to the adsorption
- \( p \) = pressure of the gas

2. **Analyze the Equation at Very High Pressure**:
At very high pressure, the term \( A p \) becomes significantly larger than 1. Therefore, we can simplify the denominator:
\[ 1 + A p \approx A p \]
This approximation is valid because \( A p \) dominates over 1 when pressure is very high.

3. **Substitute the Simplified Denominator into the Equation**:
By substituting the simplified denominator back into the equation, we have:
\[ \frac{x}{m} = \frac{A p}{A p} = 1 \]

4. **Rearranging the Equation**:
This implies that:
\[ x = m \]
This means that the amount of gas adsorbed reaches a constant value.

5. **Conclude the Behavior at High Pressure**:
As \( p \) increases further, the amount of gas adsorbed does not increase indefinitely but rather approaches a constant limiting value. This indicates that at very high pressure, the adsorption reaches saturation.

### Final Answer:
According to the Langmuir adsorption isotherm, the amount of gas adsorbed at very high pressure approaches a constant limiting value.

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