Question

calculate the number of electrons protons and neutrons in an atom of an element with atomic number 20 and mass number 40 also write their electronic configuration​

Answer 1

Atomic number = 20

Atomic number = No. of electrons

Therefore,

No. Of electrons = 20

Atomic mass = Proton + electron

40 = No. Of protons + 20

40 - 20 = No. Of protons

Therefore,

No. Of protons = 20

Atomic no. is 20

Therefore its electronic configuration = 2, 8, 8, 2

Or

$1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2}$

Hope it helps.