In kinetic theory of gases, it is assumed that molecular collisions are

Options

A. for negligible duration
B. inelastic
C. one-dimensional (head on)
D. unable to exert nutual force

Explanation

**Step-by-Step Solution:**

1. **Understanding the Kinetic Theory of Gases (KTG):**
The kinetic theory of gases provides a model to explain the behavior of gases at a molecular level. It is based on several assumptions about gas molecules, including their motion and interactions.

2. **Molecular Collisions in KTG:**
One of the key assumptions in the kinetic theory is about molecular collisions. It is assumed that these collisions occur over a negligible duration of time. This means that the time taken for a collision to happen is very small compared to the time a molecule spends traveling freely between collisions.

3. **Elastic vs. Inelastic Collisions:**
In the context of KTG, molecular collisions are considered to be perfectly elastic. This means that during the collision, the total kinetic energy of the system is conserved. Inelastic collisions, on the other hand, would involve a loss of kinetic energy.

4. **Types of Collisions:**
The theory does not limit itself to one-dimensional head-on collisions; molecules can collide at various angles (oblique collisions). Therefore, the assumption of only one-dimensional collisions is incorrect.

5. **Mutual Forces:**
It is also incorrect to say that gas molecules are unable to exert mutual forces on each other. In fact, they do exert forces during collisions, but these forces are short-lived.

6. **Conclusion:**
Based on these points, the correct statement regarding molecular collisions in the kinetic theory of gases is that they are perfectly elastic. Therefore, the correct answer is option number 1.