From the choices below, select the element that has 2 valence electrons, more than 30 neutrons but less than 70 neutrons. *
strontium (SI)
barium (Ba)
calcium (Ca)
rubidium (RD)

Ur e n d is not real

What is the question

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.