What is a major cause of variation within a
species?
A. Sexual reproduction
B. asexual reproduction
C. extinction
D. photosynthesis

Ithinks its false. tell me if im wrong

Ithink is a because if say increased in electronegativity

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.