Timed explain the presence of helium in earths crust

Asmall proportion of helium in the crust is helium that was trapped in the earth when the earth formed and has not yet escaped. most helium on earth, however, forms as a result of alpha decay of uranium and thorium. the emitted alpha particles, once they grab a couple of stray electrons, become helium atoms and can accumulate in gas reservoirs along with things such as methane.

Afraidsugar lol it’s the third one

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.