Which is the correct ground-state electron configuration for phosphorus (P), atomic number 15?

• A. $1s{2}^{}2s{2}^{}2p{6}^{}3s{1}^{}3p{4}^{}$
• B. $1s{2}^{}2s{2}^{}2p{6}^{}3s{2}^{}3p{6}^{}$
• C. $1s{2}^{}2s{2}^{}2p{6}^{}3s{2}^{}3p{5}^{}$
• D. $1s{2}^{}2s{2}^{}2p{6}^{}3s{2}^{}3p{3}^{}$

Answer: (D)