A body is standing on a merry-go-round which is rotating uniformly in a horizontal plane. His frame of reference is
A) an inertial frame
B) a non-inertial frame
C) either inertial or non-inertial
D) neither inertial nor non-inertial

Hint: According to the question the frame of reference is identified on the basis of uniform motion. Uniform motion has inertia.

Complete step by step answer:
A body is standing on a merry-go-round which is rotating uniformly in a horizontal plane. So, its frame of reference is an inertial frame. A system of coordinates whose axes can be suitably chosen is said to be a frame of reference.
In general conditions of problems related to mechanics, we solve the problems using an inertial frame. In this question, the motion gives centripetal acceleration which is present. So, any frame of reference fixed on the merry-go-round can’t be taken as an inertial frame where the acceleration will be zero and speed will be uniform.

Hence the option (A) is correct.

Additional Information:
An inertial frame of reference is a reference frame in which an object stays either at rest or at a constant velocity unless another force acts upon it. When a body does not seem to be acting in accordance with inertia, it is in a non-inertial frame of reference or accelerating.

Note:
We know that the uniform motion should be taken in the inertial frames and non-uniform motion should be taken in non-inertial frames.