Consider the following statements and arrange in the order of true/false as given in the codes.
The correct order of True/False of the following statements is :
`S_1`:Rate of diffusion and effusion of a gas increases by increasing the pressure and decreasing the temperature.
`S_2`:An ideal gas has vander waal's constant a and b equal to zero.
`S_3`:If an ideal gas is expanded adiabatically against a constant pressure then `TV^(gamma-1)`=constant

Options

A. TTF
B. FFT
C. TTT
D. FFF

Explanation

To solve the question regarding the truthfulness of the statements provided, we will analyze each statement one by one and determine if they are true or false.

### Step-by-Step Solution:

1. **Statement S1**: "Rate of diffusion and effusion of a gas increases by increasing the pressure and decreasing the temperature."
- **Analysis**: The rate of diffusion and effusion of a gas is described by Graham's law, which states that the rate is inversely proportional to the square root of the molar mass and directly proportional to the pressure and inversely proportional to the temperature. Increasing the pressure increases the rate, while decreasing the temperature also increases the rate (as it reduces the kinetic energy of the gas molecules). Therefore, this statement is **True**.

2. **Statement S2**: "An ideal gas has Van der Waals constant a and b equal to zero."
- **Analysis**: The Van der Waals equation accounts for the volume occupied by gas molecules and the attractive forces between them. For an ideal gas, these interactions and volumes are negligible, which means that the constants 'a' (which accounts for intermolecular forces) and 'b' (which accounts for the volume occupied by gas molecules) are indeed equal to zero. Thus, this statement is **True**.

3. **Statement S3**: "If an ideal gas is expanded adiabatically against a constant pressure then TV^(gamma-1) = constant."
- **Analysis**: In an adiabatic process, the relationship for an ideal gas is given by \( PV^{\gamma} = \text{constant} \) (where γ is the heat capacity ratio). However, if the gas is expanded against a constant pressure, it is not a purely adiabatic process, and the correct relationship should be \( PV^{\gamma} = \text{constant} \) instead of \( TV^{\gamma-1} = \text{constant} \). Therefore, this statement is **False**.

### Conclusion:
The order of truthfulness for the statements is:
- S1: True
- S2: True
- S3: False

Thus, the correct order of True/False for the statements is: **T, T, F**.

### Final Answer:
The correct code for this question is **TTF**.