Why is not an atom electrically charged though it contains electrons & protons?

It depends upon the number of electrons and the number of protons in the atom. If it has the same number of both, then it is neutral. If it is missing one or more electrons, that is one or more protons than electrons. it is a positively charged ion, and if it has one or more extra electrons, it is a negatively charged ion. How many electrons an atom can have depends on what element it is, specifically, the number of electrons in the outer shell of the atom.