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

a) hydrogen and helium

b) sodium and potassium

c) carbon and oxygen

d) boron and beryllium

Answer : The correct option is, (B) sodium and potassium

Explanation :

Valence electrons : Valence electrons are those electrons which are present in the outermost shell of the element.

As we know that,

Option (A) :

Element = Hydrogen

Atomic number = Number of electrons = 1

The electronic configuration is,

The number of valence electrons = 1

Element = Helium

Atomic number = Number of electrons = 2

The electronic configuration is,

The number of valence electrons = 2

Option (B) :

Element = Sodium

Atomic number = Number of electrons = 11

The electronic configuration is,

The number of valence electrons = 1

Element = Potassium

Atomic number = Number of electrons = 19

The electronic configuration is,

The number of valence electrons = 1

Option (C) :

Element = Carbon

Atomic number = Number of electrons = 6

The electronic configuration is,

The number of valence electrons = 4

Element = Oxygen

Atomic number = Number of electrons = 8

The electronic configuration is,

The number of valence electrons = 6

Option (D) :

Element = Boron

Atomic number = Number of electrons = 5

The electronic configuration is,

The number of valence electrons = 3

Element = Beryllium

Atomic number = Number of electrons = 4

The electronic configuration is,

The number of valence electrons = 2

From this we conclude that, the sodium and potassium are the elements have the same number of valence electrons.

Hence, the correct option is, (B)