3d < 4s is NOT a correct ordering of subshells in the periodic table because 4s is at a lower energy level than 3d.
According to the Aufbau principle, The electron configuration of an element tells how electrons of that element are arranged in thier subshells from their lowest energy state before the highest energy state.
For example, before a 2s subshell can be occupied, A 1s subshell must be filled.
The orbitals are filled in this order:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s,
For example, Na (sodium) with 11 atomic number is written as 1s2 2s2 2p6 3s1
Therefore,
2p < 3s True
3d < 4p True
3d < 4s False
4s < 4p True
See more here: brainly.com/question/19221869
