Which element has six valence electrons in each of its atoms in the ground state?

(1) Se

(2) As

(3) Kr

(4) Ga

Answer is: selenium (Se).

1) electron configuration: ₃₄Se 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4sp⁴.

2) ₃₃As 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4sp³.

3) ₃₆Kr 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4sp⁶.

4) ₃₁Ga 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4sp¹.

Valence electrons of selenium are 4s²4sp⁴.