Correct order of atomic radii is

The correct order of atomic size of C, N, P, S follows the order N<C<S<P.

 On going from C to N, the nuclear charge increases. But the additional electron is added in the same energy level. Hence, due to shielding effect, the effective nuclear charge increase. The attraction of the nucleus for the valence electrons increases. Hence, the atomic size decreases. 

The atomic size of C is larger than that of N. For the same, reason, the atomic size of P is larger than that of S. The atomic size of S is larger than that of C as the electron is added to new energy level.