What element has the electron configuration Ar 4s1?

The element with the electron configuration Ar 4s1 is potassium (K).

Here’s a breakdown of this configuration:

• Ar stands for argon, which has an atomic number of 18. This means that the first 18 electrons of potassium fill the electron shells up to argon.
• The 4s1 indicates that there is one electron in the 4s orbital, which corresponds to potassium’s atomic number of 19.

In summary, potassium is the first element in the fourth period of the periodic table and has its outermost electron in the 4s subshell, which is why it’s represented as Ar 4s1.