Question: what is the major difference between a 1s and 2s orbital?
Answer: 1s is the lowest possible energy state for an electron while the 2s is not ( because 1s is !) The 1s orbital is smaller in size than the 2s orbital. The first two electrons of any atom are present in the 1s while the next three go to 2s. 1s orbital is closest to the nucleus of an atom while the 2s comes next .