Which subshell is likely to be filled before the rest of the subshells at a particular energy level

Explanation:

According to Aufbau's principle, in the ground state of an atom electrons will first enter into the lowest energy level orbital.

Hence, 1s sub-shell will be filled before 2s sub-shell is occupied.

A sub-shell that is closer to the nucleus and that has lowest energy is the "s" sub-shell.

So, an electron will most likely enter into first shell, that is, n = 1. Hence, 1s will be the sub-shell in which the electron will enter first.

For example, electronic configuration of lithium atom is .

Therefore, we can conclude that 1s subshell is likely to be filled before the rest of the subshells at a particular energy level.

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