Question

Why 4s orbital lower energy than 3d orbital for two marks answer?

Answer 1

by auf bau rule of energy comparison
energy is given by n+l
for 4s energy is 4+0=4
for 3d energy is 3+2=5
thus 3d has more energy than 4s orbital...

Answer 2

Hey mate, here is your answer :

We know that the 4s electrons are lost first during ionisation. The electrons lost first will come from the highestenergy level, furthest from theinfluence of the nucleus. So the 4s orbital must have a higher energy than the 3d orbitals.

Hope this answer helps you...