To analyze the statements according to the kinetic theory of gases, we will evaluate each statement one by one.
### Step 1: Evaluate Statement I
**Statement I:** Collisions are always elastic.
According to the kinetic theory of gases, collisions between gas molecules and between molecules and the walls of the container are considered elastic. This means that there is no loss of kinetic energy in these collisions. Therefore, Statement I is **True**.
### Step 2: Evaluate Statement II
**Statement II:** Heavier molecules transfer more momentum to the wall of the container.
Momentum is defined as the product of mass and velocity (p = mv). Heavier molecules, having greater mass, will indeed transfer more momentum to the walls of the container upon collision, assuming they have the same velocity as lighter molecules. Therefore, Statement II is **True**.
### Step 3: Evaluate Statement III
**Statement III:** Only a small number of molecules have very high velocity.
In a gas, the distribution of molecular speeds follows a statistical distribution (Maxwell-Boltzmann distribution). While there are some molecules with very high velocities, the majority of molecules will have velocities around the average value, with only a small fraction having extremely high speeds. Therefore, Statement III is **True**.
### Conclusion
All three statements (I, II, and III) are true according to the kinetic theory of gases. However, the question asks for pairs of statements. The possible pairs are:
1. I and II
2. I and III
3. II and III
Since all statements are true, any combination of two statements is valid. However, if we are to select pairs, we can choose any of the pairs mentioned.
### Final Answer
The correct answer is that all statements are true, and thus, any combination of two statements is valid.
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