Question

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

Answer 1

Answer: Option (a) is the correct answer.

Explanation:

Valence electrons are the electrons present in the outermost shell of an atom.

Atomic number of beryllium is 4 and its electronic distribution is 2, 2. This means there are only two shells of electrons.

Whereas atomic number of sodium is 11 and its electronic distribution is 2, 8, 1.  This means there are three shells of electrons.

Also there is one more valence electron in sodium as compared to beryllium.

Thus, we can conclude that out of the given options the element X is sodium (Na).

Answer 2

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. The correct answer is "Sodium(Na). Sodium has three shells while Beryllium has two; Beryllium has one more valence electron compared to Sodium.