The overtone frequencies may be a simple multiple of the fundamental frequency (ν = nν₀) or an odd multiple of the fundamental frequency {ν = (2n+1)ν₀} depending upon whether it is an open organ pipe or closed organ pipe.

Since it is not given whether the pipe is open or closed, we cannot be sure that the first overtone is 400 Hz. So the option A is not true.
The first overtone may be 400 Hz if the pipe is open because it is the first even multiple of the fundamental frequency 200 Hz. Option B is true. The first overtone may be 600 Hz if the pipe is closed because it is the first odd multiple of the fundamental frequency 200 Hz (3*200 Hz). Option B is true. Since 600 Hz is an even as well as odd multiple of 200 Hz, it is an overtone whether the pipe is open one or closed. Option D is true.