For the electrons of oxygen atom, which of the following statements is correct ? (a) Zeff for an electron in a 2s orbital is the same as Zeff for an electron in a 2p orbital (b) An electron in the 2s orbital has the same energy as an electron in the 2p orbital (c) Zeff for electron in 1s orbital is the same Zeff for an electron in a 2s orbital (d) The two electrons present in the 2s orbital have spin quantum number ms but of opposite sign