Here's why:

* Electron Configuration: Antimony's electron configuration is [Kr] 4d¹⁰ 5s² 5p³.

* Valence Shell: The outermost shell (the one with the highest principal quantum number) is the 5th shell.

* Valence Electrons: The electrons in the valence shell (5s² 5p³) are the valence electrons, totaling 2 + 3 = 5.