Why is there less energy required to ionise 3s1 than 4s1 orbitals?

Sorry if the question above doesn't make sense, but here is the original question:

The electronic configurations, X and Y, for two uncharged atoms of Na are as follows:

X: 1s2 2s2 2p6 3s1
Y: 1s2 2s2 2p6 4s1

Which of the following statements is true?

The answer is:

Less energy is required to ionise Y compared to X.


I would've thought that 4s1 would require more energy, so I'm really confused.

Thanks.

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