The correct order of radii is .
The size of isoelectronic species depends on the nuclear charge.
As the nuclear attraction increases the electrons are strongly bound to the nucleus.
all have the same no. of e-but as atomic number increases ( ) nuclear charge also increases.

Now, as compared to O, F has more ratio of nuclear charge per electron.
Among the isoelectronic species, the size increases as the negative charge increases.

So, the nuclear charge per electron increases, and they are strongly bound to the nucleus, decreasing the size.