Explanation:

- The average of P and Q is given as $(P+Q)/2$.

- The average of Q and R is given as $(Q+R)/2$.

- It's given that the difference between these averages is 25.

- Formulating the equation:

$$((P+Q)/2)-((Q+R)/2)=25$$

- Simplifying further:

$$(P+Q-Q-R)/2=25$$

- This simplifies to:

$$(P-R)/2=25$$

- Solving for $P-R$, we multiply both sides by 2:

$$P-R=50$$

- Option 2: 50 is the correct answer.