Question

Assertion: Lithium is the weakest reducing agent among alkali metals.
Reason: In alkali metals ionization energy decreases down the group.

Read the above assertion and reason and choose the correct option regarding it.
(A) Both assertion and reason are correct and reason is the correct explanation for assertion.
(B) Both assertion and reason are correct and reason is not the correct explanation for assertion.
(C) Assertion is incorrect but reason is correct.
(D) Both assertion and reason are incorrect.

Answer 1

Hint: In order to answer this question, you should know that in alkali metals the ionization energy decreases down the group with increasing atomic size, which leads to addition of new atomic shells.

Complete step by step answer:
As we know alkali metals are very good reducing agents because of their great tendency to lose electrons. An element which acts as a reducing agent must have low ionization energy. Alkali metals act as strong reducing agents as their ionization energy values are low. As we already know ionization decreases on moving down from Li to Cs, the reducing property increases in the same order. Thus, Li is the weakest reducing agent while Cs is the strongest reducing agent among alkali metals in free gaseous state.

The oxidation potential value is nothing but the tendency of an element to lose electrons in solution is measured by its oxidation potential value. As we know, alkali metals have high oxidation potential values, these are strong oxidizing agents.

Lithium being small in size has high ionization enthalpy and because of its small size it is extensively hydrated and has a very high hydration enthalpy. Thus lithium has a greater tendency to lose electrons in solution than other alkali metals. Therefore, lithium is the strongest reducing agent.

Hence, the assertion is incorrect but the reason is correct. Therefore, option C is the required answer.

Note: You should know that lithium and magnesium form monoxides when heated in air or oxygen while other alkali metals form peroxides or super-oxides.