Question

Assertion: Phosphorous, sulphur and chlorine are electronegative elements of the periodic table.
Reason: Phosphorus, sulphur and chlorine have incomplete octet and have tendency to gain electrons.
(A) Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
(B) Both Assertion and Reason are correct and Reason is not the correct explanation of Assertion.
(C) Assertion is correct but reason is incorrect.
(D) Both Assertion and Reason are incorrect.

Answer 1

Take a look at the periodic table. Locate the blocks in which the elements given in the question lies. We know as the size of the atom decreases, electronegativity increases. Write their electronic configuration and then draw a conclusion.

Complete step by step answer:
- Phosphorus belongs to the nitrogen family. Sulphur belongs to chalcogens and chlorine is a halogen. All the three elements, phosphorus, sulphur and nitrogen are p-block elements.
- We know that, as we move from left to right in a periodic table, atomic size decreases because electrons are added in the same shell. As the atomic size decreases, electronegativity increases.
- Electronegativity is the property of an atom to accept electrons in order to gain stability by completing the octet and attaining the noble gas configuration.
- Let’s write the electronic configuration of phosphorus, sulphur and nitrogen.
${}^{15}P=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{3}}$
${}^{16}S=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{4}}$
${}^{17}Cl=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{5}}$

- In all three atoms, octet is incomplete. Therefore, they will have a strong tendency to attract electrons. Hence, phosphorus, chlorine and sulphur will be electronegative in nature.
- Therefore, the assertion is true and the reason is also true. Reason is the correct explanation of assertion.
So, the correct answer is “Option A”.

Note: Remember fluorine is the most electronegative element in the periodic table and cesium is the most electropositive element in the periodic table. Nitrogen family, chalcogens and halogens are electronegative in nature and alkali metals and alkaline earth metals are electropositive in nature. Metals are electropositive in nature.