Question:

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R

Assertion (A) : Sodium reacts with oxygen to form \(Na _{2} O _{2}\) but potassium reacts with oxygen to form \(KO _{2}\). 

Reason (R) : Potassium is more reactive metal than sodium.

In the light of the above statements, choose the correct answer from the options given below

Updated On: Apr 6, 2023
  • If both Assertion and Reason are true and Reason is correct explanation of Assertion.
  • If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  • If Assertion is true but Reason is false.
  • If both Assertion and Reason are false.
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The Correct Option is B

Solution and Explanation

It is because of bigger size of $K ^{+}$than $Na ^{+}$, a weak positive field arises around it which cannot prevent peroxide ion $\left( O _{2}^{2-}\right)$ to combine with another oxygen atom to form superoxide, $O _{2}^{-}$.
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Concepts Used:

Group 1 Elements

Group one of alkali metals is s-block elements with just one electron in their s-orbital. They are are alkali metals. They are named so because of the alkaline nature of the hydroxides and oxides.

Alkali metals are characterized by one s-electron in the valence shell of their atoms.

Alkali metals have a corresponding [Noble gas] ns1 electronic configuration. They occupy the first column of the periodic table. Alkali elements are:

  • Lithium(Li)
  • Sodium(Na)
  • Potassium (K)
  • Rubidium (Ru)
  • Cesium (Cs)
  • Francium (Fr)

They have occupied successive periods from first to seven. Francium is a radioactive element with very low half-life.

Electronic Configuration:

  • Alkali metals have one electron in their valence shell.
  • The electronic configuration is given by ns1. For example, the electronic configuration of lithium is given by 1ns1 2ns1.
  • They tend to lose the outer shell electron to form cations with charge +1 (monovalent ions).

This makes them the most electropositive elements and due to the same reason, they are not found in the pure state.