Question

Which of the following elements shows variable valency?

• A. Nickel
• B. Sodium
• C. Helium
• D. Carbon

Answer 1

The correct option is A

Nickel

The explanation for the correct option:

Option A

• Some elements have different combining capacities while forming different molecules and compounds and therefore they exhibit more the one valency which is called variable valency.
• These elements can donate or accept different numbers of electrons depending on the conditions and they are said to have different valency.
• Nickel shows three types of valencies i.e. 2, 3, and 4 depending upon the different conditions while forming various compounds. Therefore, nickel shows variable valency.

The explanation for the incorrect options:

Option B

The electronic configuration of sodium is 2,8,1. It can donate only one electron to achieve a noble gas configuration therefore it shows only one type of valency i.e 1.

Option C

Helium has 2 electrons in its valence shell and exhibits a stable noble gas configuration. Therefore valency of helium is zero.

Option D

The electronic configuration of carbon is 2,4. It has 4 electrons in its valence shell and shows one type of valency i.e. 4.

Therefore, option (a) is the correct answer.