The major difference between a 1s orbital and a 2s orbital is that The 2s orbital has a slightly different shape.
The 2s orbital is at a higher energy level.
The 2s orbital can hold more electrons.
The 1s orbital can have only one electron.

The 2s orbital is at a higher energy level.

Explanation:

1s and 2s are the sub-orbitals that are located in an atom. They are nearest to the nucleus and are found on the s sub-orbital. The difference between 1s and 2s is the difference in their level of energy. 1s has low energy as compared to 2s. 1s orbital has the lowest energy because it is located closed to the nucleus. 2s orbital has higher energy than 1s because it's orbit is larger than 1s.

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