What is the ground-state electron configuration of potassium (K, atomic number 19)?

• A. $1s_{2}2s_{2}2p_{6}3s_{2}3p_{5}4s_2$
• B. $1s_{2}2s_{2}2p_{6}3s_{2}3p_{6}4s_1$
• C. $1s_{2}2s_{2}2p_{6}3s_{2}3p_{6}3d_1$
• D. $1s_{2}2s_{2}2p_{6}3s_{2}3p_6$

Answer: (B)