In the formation of NaCl, Na gets oxidised because it loses an electron, while Cl gets reduced because it gains an electron.
But how does this concept work in the case of covalent compounds, especially those compounds that have non-polar bonds?
For example, according to my textbook, in the formation of methane Hydrogen is getting oxidised from state 0 to 1, while Carbon is getting reduced from state 0 to -4.
But how is hydrogen losing an electron here? Doesn't it gain an electron due to sharing? C-H bonds are non polar so we cannot say that carbon pulls hydrogen's electrons towards it either right?