An atom has an electron configuration of
1s², 2s², 2p⁶, 3s², 3p3
how many valence electrons does the atom have?

5

Explanation:

The full electronic configuration of the element is

1s²2s²2p63s²3p³

The total number of electrons = addition of the index

That is number of electrons = 2+2+6+2+3 = 15

Therefore the atomic number of the element is 15.

Name of element with atomic number 15 is Phosphorus with symbol P

Number of electrons in the atom of the element is 15.

Using KLMN configuration = 2:8:5

Therefore number of valence electrons is 5

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the electron configuration that you gave me has 16 electrons ergo it has 16 protons ergo it is the element sulfur.