What is wrong with writing the electron configuration of a ground state atom as 1s2 2s2 2p6 3s2 3p6 4s2 4d1?

4d - orbital makes the given electronic configuration wrong.

Explanation:

The order of electronic configuration is written as;

1s²

2s²      2p⁶

3s²      3p⁶      3d¹⁰

4s²      4p⁶      4d¹⁰        4f¹⁴

5s²      5p⁶      5d¹⁰        5f¹⁴

6s²      6p⁶      6d¹⁰        6f¹⁴

7s²      7p⁶       7d¹⁰        7f¹⁴

In order of energy level from the lowest to the highest, the configuration of the given atom in ground state can be written as;

1s²    2s²   2p⁶   3s²   3p⁶   4s²  3d¹, when compared to the given configuration, 4d orbital makes the given configuration wrong, because the next orbital after 4s is 3d.