[tex]{ \huge{ \bold{ \mathfrak{Answer}}}}[/tex]
The answer is CQ.
[tex]{ \huge{ \bold{ \mathfrak{ Explanation}}}}[/tex]
As it is given that PQ is a diameter ,C is the centre and P, Q and S are the points are on the circle.
According to this information given, I have provided a pic which can clear your doubts.
As you know that PQ is a diameter. Therefore, radius is the half of diameter.
If any other query, you can surely ask!
[tex] <marquee > Thank you :) [/tex]