Any reaction that absorbs 150 kcal of energy can be classified as
a. activated.
b. exothermic.
c. oxidation.
d. endothermic

The answer should be (D) endothermic reaction.

Reason : -  Reactions in which energy is absorbed are called endothermic reactions. In your provided question, 150 kcal energy is being absorbed, and thus, we can say that it is an endothermic reaction. 

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.