An atom of element X has one more shell of electrons than an atom of beryllium, but it has one less valence electron than beryllium. Which element is element X?

Question

sodium (Na)
boron (B)
magnesium (Mg)
lithium (Li)

Answer 1

The element X in this case would be boron (B).

Beryllium (Be) has 4 electrons and 2 valence electrons, while boron (B) has 5 electrons and 3 valence electrons. Therefore, element X, which has one more shell of electrons than beryllium but one less valence electron, is boron (B).