What is the element with a valence electron configuration of 4s24p6?

Krypton (Kr)

Explanation:

First of all, the valence electron configuration shows the total number of electron an atom have. Let's write this in a better way:

4s² 4p⁶

The superscript numbers represents the electron of the atom. In this case, we can see that this element has 8 electrons, which means it has the maximum electrons an element can have.

The only elements in the periodic table that has the maximum number of electrons their valence cap, are the noble gases. The noble gases are Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe).

Now how do we know which of the four it is?

This is actually pretty easy, the number of the cap, represents the period of the element. In other words, if the valence configuration cap number, (which has the orbitals s, p, d or f) has the number 2, means that the element is on period 2. In this case, we can see that the valence cap is 4, so this element belongs to period 4. The last element of this period is Krypton, therefore, the element with these valence electron, is Krypton.