A compound is formed when two or more elements combine in definite proportions. In the given scenario we have carbon and hydrogen atoms.
The valence electron configuration of C = 2s²2p²
H = 1s¹
There are 4 valence electrons in carbon; one paired (2s) and two unpaired (2p). Promotion of a 2s electron to a 2p orbital leaves 4 unpaired electrons which can combine with 4 H atoms to form a stable compound: CH4
Ans: (a) CH4, because four electron pairs are shared between carbon and hydrogen.