Question

it is said that no of protons = no of electrons..
so when a element donates it electrons from the outer most shell in order to attain stability..thn the no of electrons will be less than the no of protons?!...so what about our previous case that it's equal!!
ex- if carbon has 6 electrons...and 4 electrons in outer most shell so it donates 4..so it has 2 electrons left that is not equal to no of protons!?

Answer 1

In an atom, number of electrons = number of protons.
But when an atom donates or gains electrons, it is no longer an atom. It becomes ion.
And ions have number of protons not equal to number of electrons.
But atom always have both number equal.

Answer 2

Number of protons is equal to number of electrons in case of a neutral atom.
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Sometimes an element donates electrons from its outermost shell to gain stability and form bonds with other elements. When it donates an electron, it becomes positively charged and hence it is longer a neutral atom. it becomes a positive ion.

Similarly if an element gains electron to form bonds, it becomes a negative ion.

In ions, number of protons is never equal to number of electrons.

So the case "no of protons = no of electrons" holds only in neutral atoms.
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The example you have taken is not possible under normal conditions. An atom generally can lose or gain upto 3 electrons.

Losing or gaining 4 electrons is very difficult or maybe impossible under normal conditions. So Carbon doesn't lose or gain 4 electrons.
It forms bond by sharing the electrons with other atoms.

Sharing of electrons leads to formation of covalent bonds whereas losing and gaining of electron is involved in formation of ionic bonds.