Question

Name an element that has same number of electrons in 1st and 4th shell as well as 2nd and 3rd shell?

Answer 1

Electrons in 1st orbit : 2

so, 4th orbit will also have 2 electrons

number of electrons in 2nd orbit= no. in 3rd orbit

we know, that an electron will only move to the 3rd orbit when 2 nd orbit will be filled (8 electrons)

so, number of electrons in 2nd and 3rd orbits = 8

All in all, electronic config of atom: 2, 8, 8, 2

atomic number= 2 + 8 + 8 + 2= 20

so, element with atomic number is: Calcium (Ca)