Which of these pairs of elements have the same number of valence electrons?

phosphorus (p) and chlorine (cl)

berylium (be) and calcium (ca)

chlorine (cl) and helium (he)

oxygen (o) and carbon (c)

Option (b) is the correct answer.

Explanation:

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

So, number of valence electrons of given elements will be as follows.

Phosphorous (P) - atomic number is 15, valence electrons are 5.

Chlorine (Cl) - atomic number is 17, valence electrons are 7.

Beryllium(Be)  - atomic number is 4, valence electrons are 2.

Calcium (Ca) - atomic number is 20, valence electrons are 2.

Helium (He) - atomic number is 2, valence electrons are 0.

Oxygen (O) - atomic number is 16, valence electrons are 6.

Carbon (C) - atomic number is 6, valence electrons are 4.

Therefore, we can conclude that berylium (Be) and calcium (Ca) is the pair of elements that have the same number of valence electrons.