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

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

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