For the electrons of oxygen atom, which of the following statements is correct?

(A)Electrons in 2s and 2p- orbitals have different screening effect. Hence their $Z_{eff}$     is different  $Z_{eff}$ of 2s- orbitals > $Z_{eff}$ of 2p-orbitals. Therefore, it is not correct

(B) Energy of 2s – orbitals < energy of 2p – orbitals

(C) $Z_{eff}$  of 1s – orbitals  $\ne$$Z_{eff}$ of 2s – orbitals. Hence, it is correct

(D)For the two electrons of 2s – orbitals, the value of  $m_s$ is $+\frac{1}{2}and-\frac{1}{2}$

  Hence, it is correct