Amodel of the solar system with the sun at the center is said to be heliocentric.

true or false

True is the correct because helio means sun in greek  and the sun is in the center of our universe

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.

High-energy and unstable.