The answer is letter d. it has only 2 electrons in its first shell and 4 in the second shell. Basing from the electronic configuration of the carbon atom, the "s" orbital of carbon atom is completely filled leaving now the "p" orbitals partially filled. Thus in this case, carbon atom has four (4) valence electrons.
Up to the the population carrying capacity the the population will increase to give a perfect balance and when the population will be much then the population will decrease.
