Question

If the mass number of an atom is $A = 40$ and its electron configuration is$1s^{2},\mspace{6mu} 2s^{2},\mspace{6mu} 2p^{6},\mspace{6mu} 3s^{2},\mspace{6mu} 3p^{6}$, the number of neutrons and protons in its nucleus will be.

• A. 22, 18
• B. 18, 22
• C. 20, 20
• D. 18, 18

Answer 1

Answer: (A)

22, 18

Answer 2

Number of protons = 2 + 2 + 6 + 2 + 6 = 18

Number of neutrons = 40 – 18 = 22.