Gallium atoms have the ground-state electron configuration [Ar] 3d¹⁰ 4s² 4p¹. Which of the following lists the peaks from these three subshells in order of increasing binding energy (lowest to highest)?
a) 3d < 4s < 4p
b) 4s < 4p < 3d
c) 4p < 4s < 3d
d) 4p < 3d < 4s