N = 32, A = 24, S = 8.
In constructing the Lewis dot formula for phosgene (COCl2) with carbon (C) as the central atom, we first calculate the quantities for N (needed electrons), A (available electrons), and S (shared electrons). Phosgene consists of one carbon atom, one oxygen atom, and two chlorine atoms. The needed electrons (N) are determined by considering the octet rule for each atom, where carbon needs 4 electrons, oxygen needs 6, and each chlorine needs 7. The total needed electrons (N) is then calculated as 4 + 6 + 7 + 7 = 24.
The available electrons (A) are the sum of valence electrons for each atom, considering carbon with 4, oxygen with 6, and chlorine with 7 each. The total available electrons (A) is 4 + 6 + 7 + 7 = 24.
Shared electrons (S) represent the number of electrons involved in bonding, and it is determined by subtracting the total available electrons (A) from the total needed electrons (N). Therefore, S = N - A, which is 24 - 24 = 0.
Among the given choices, N = 32, A = 24, S = 8 aligns with the correct calculation for phosgene's Lewis dot structure, ensuring that each atom satisfies the octet rule, and the central carbon atom forms double bonds with both oxygen and chlorine atoms, resulting in a stable molecular arrangement.