Assertion Total internal energy of oxygen gas at a given temperature is E of this energy `3/5` E is rotational kinetic energy.
Reason Potantial energy of an ideal gas is zero.

Options

A. If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are correct but Reason is not the correct explation os Assertion.
C. If Assertionis true bur Reason is false.
D. If Assertion is false but Reason is true.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understanding the Assertion
The assertion states that the total internal energy (U) of oxygen gas at a given temperature is E, and that 3/5 of this energy is rotational kinetic energy.

For a diatomic gas like oxygen, the degrees of freedom (f) are:
- 3 translational degrees of freedom
- 2 rotational degrees of freedom

The total degrees of freedom for a diatomic gas is:
\[ f = 3 + 2 = 5 \]

The formula for the internal energy (U) of an ideal gas is given by:
\[ U = \frac{f}{2} nRT \]
Where:
- \( n \) = number of moles
- \( R \) = universal gas constant
- \( T \) = temperature in Kelvin

For oxygen (O2), substituting \( f = 5 \):
\[ U = \frac{5}{2} nRT \]

### Step 2: Calculating Rotational Kinetic Energy
The rotational kinetic energy (K_rot) for a diatomic gas, which has 2 rotational degrees of freedom, is given by:
\[ K_{rot} = \frac{2}{2} nRT = nRT \]

To express this in terms of the total internal energy (E):
Since \( U = \frac{5}{2} nRT \), we can relate \( nRT \) to \( U \):
\[ nRT = \frac{2}{5} U \]

Now, substituting this back into the equation for rotational kinetic energy:
\[ K_{rot} = nRT = \frac{2}{5} U \]

### Step 3: Finding the Fraction of Rotational Kinetic Energy
To find the fraction of the total internal energy that is rotational kinetic energy:
\[ \frac{K_{rot}}{U} = \frac{\frac{2}{5} U}{U} = \frac{2}{5} \]

Thus, the assertion that 3/5 of the total internal energy is rotational kinetic energy is incorrect.

### Step 4: Understanding the Reason
The reason states that the potential energy of an ideal gas is zero. This is true because, in the kinetic theory of gases, it is assumed that there are no intermolecular forces acting between the gas molecules, which means that potential energy can be neglected.

### Conclusion
- The assertion is **false** because 3/5 of the internal energy is not rotational kinetic energy; it is actually 2/5.
- The reason is **true** because the potential energy of an ideal gas is indeed considered to be zero.

Thus, the correct answer is that the assertion is false and the reason is true.

### Final Answer
- Assertion: False
- Reason: True