[Indranil (OP)]

In this reaction, How many electrons carbon anion has 7 or 8? I mean C- has 7 electrons or 8 electrons and H+ has one proton, how to H+ ion combine with H3C- ion to form CH4 because H+ ion needs 2 electrons? I am confused. Please show the mechanism.

[chiralSPO]

H⁺ has no electrons (just one proton--this reaction is a "protonation")
There are a total of 10 electrons in CH₃^– (6 from the C atom, 1 for each of the 3 H atoms, and 1 extra electron for the negative charge.) Two of these electrons form the inner "core" of the carbon atom (a full 1s orbital), and the remaining 8 electrons are all in the "valence." We can think of there bing 2 electrons in each of the 3 C-H bonds, and another 2 electrons as a lone pair on C.

When the H⁺ comes close to the electrons in the lone pair, it will be attracted electrostatically, and will get closer and closer until it is trapped and "bonded." The product molecule, CH₄ is neutral and has 10 electrons (the proton didn't bring any electrons with it.) The mechanism can be represented by a single curved and double-headed arrow, pointing from the lone pair of the methyl anion (CH₃^– and going to the proton (H⁺).

[Indranil (OP)]

H⁺ has no electrons (just one proton--this reaction is a "protonation")
There are a total of 10 electrons in CH₃^– (6 from the C atom, 1 for each of the 3 H atoms, and 1 extra electron for the negative charge.)

Where do the carbon get the extra electron for the negetive charge?

[Kryptid]

Where do the carbon get the extra electron for the negetive charge?

Presumably by taking it from some other atom before it became involved in the reaction that this thread is about.