Water boils at a lower temperature at high
altitudes. The most likely explanation for
this is that at high altitudes

At higher altitudes the density of the air is lower which means that there is less air pushing down in the water molecules. This allows the water molecules to move faster and get to their boiling point.

Ibelieve your answer is true 

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.