Correct Answer: P × Q – R

Solution : Let's check the options –
First option: P ÷ R – Q
According to the given expression, the family tree will be as follows –

Here, the quadrilateral represents the male, and the circular figure represents the female in the figure. From the above family tree, it is evident that P is the sister of R.
Second option: P × Q ÷ R
According to the given expression, the family tree will be as follows –

Here, the quadrilateral represents the male, and the circular figure represents the female in the figure. From the above family tree, it is evident that P is the mother of R.
Third option: Q × P – R
According to the given expression, the family tree will be as follows –

Here, the quadrilateral represents the male, and the circular figure represents the female in the figure. From the above family tree, it is evident that P is the father of R.
Fourth option: P × Q – R
According to the given expression, the family tree will be as follows –

Here, the quadrilateral represents the male, and the circular figure represents the female in the figure. From the above family tree, it is evident that P is the paternal grandmother of R.

So, only the expression in the fourth option satisfies the relation given in the question. Hence, the fourth option is correct.