Question

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 1

B) sodium and potassium (1 valence electron)

Answer 2

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,
`1s^1`

The number of valence electrons = 1

Element = Helium

Atomic number = Number of electrons = 2

The electronic configuration is,
`1s^2`

The number of valence electrons = 2

Option (B) :

Element = Sodium

Atomic number = Number of electrons = 11

The electronic configuration is,
`1s^22s^22p^63s^1`

The number of valence electrons = 1

Element = Potassium

Atomic number = Number of electrons = 19

The electronic configuration is,
`1s^22s^22p^63s^23p^64s^1`

The number of valence electrons = 1

Option (C) :

Element = Carbon

Atomic number = Number of electrons = 6

The electronic configuration is,
`1s^22s^22p^2`

The number of valence electrons = 4

Element = Oxygen

Atomic number = Number of electrons = 8

The electronic configuration is,
`1s^22s^22p^4`

The number of valence electrons = 6

Option (D) :

Element = Boron

Atomic number = Number of electrons = 5

The electronic configuration is,
`1s^22s^22p^1`

The number of valence electrons = 3

Element = Beryllium

Atomic number = Number of electrons = 4

The electronic configuration is,
`1s^22s^2`

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)