In the following diagram, police represents circle, corrupt represents triangle, poet represents square and married represents rectangle

The number representing unmarried police officers who are not corrupt but are poets is

8

As per condition:

Police represents circle,

Corrupt represents triangle,

Poet represents square and

Married represents rectangle.

So, unmarried police officers who are not corrupt but are poets is:

Number of person, who are in circle (police), not in rectangle (Unmarried), not in triangle (not corrupt) but in square (poet).

Thus, we need that number, which is common in circle and square only.

That is number 8.