Which electron configuration contains three half-filled orbitals? (A) 1s2 2s2 2p6 (B) 1s2 2s2 2p5 (C) 1s2 2s2 2p3 (D) 1s2 2s2 2p4?

1s subshell contains only one orbital, i.e. 1s orbital.
2s subshell contains only one orbital, i.e. 2s orbital.
2p subshell contains three orbitals, namely 2px, 2py and 2pz orbitals.

The electronic configuration of the four options can be rewritten as :
(A) 1s² 2s² 2px² 2py² 2pz² (NO half-filled orbital)
(B) 1s² 2s² 2px² 2py² 2pz¹ (ONE half-filled orbital)
(C) 1s² 2s² 2px¹ 2py¹ 2pz¹ (THREE half-filled orbitals)
(D) 1s² 2s² 2px² 2py¹ 2pz¹ (TWO half-filled orbital)

The answer : (C) 1s² 2s² 2p³

C