At constant pressure , the volume of fixed mass of an ideal gas is directly proportional to

Options

A. Absolute temperature
B. Degree contigrade
C. Degree Fahrenheit
D. None

Explanation

To solve the question, we need to understand the relationship between the volume of an ideal gas and its temperature at constant pressure. This relationship is described by Charles's Law.

### Step-by-Step Solution:

1. **Understand the Ideal Gas Law**: The ideal gas law is given by the equation:
\[ PV = nRT \]
where \( P \) is the pressure, \( V \) is the volume, \( n \) is the number of moles, \( R \) is the gas constant, and \( T \) is the temperature.

2. **Identify the Conditions**: The question states that the pressure is constant and we have a fixed mass of gas. This means that \( P \) and \( n \) are constant.

3. **Rearranging the Ideal Gas Law**: Since \( P \) and \( n \) are constant, we can rearrange the ideal gas law to focus on volume and temperature:
\[ V = \frac{nRT}{P} \]
Since \( n \), \( R \), and \( P \) are constants, we can see that volume \( V \) is directly proportional to temperature \( T \):
\[ V \propto T \]

4. **Temperature in Kelvin**: It is important to note that temperature \( T \) must be measured in Kelvin for this relationship to hold true. The Kelvin scale is the absolute temperature scale, where 0 Kelvin is absolute zero.

5. **Conclusion**: Therefore, at constant pressure, the volume of a fixed mass of an ideal gas is directly proportional to the absolute temperature (in Kelvin).

### Final Answer:
The volume of a fixed mass of an ideal gas at constant pressure is directly proportional to **absolute temperature**.