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Chemistry Question 53 – NEET-UG 2023

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Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R : Assertion A : Metallic sodium dissolves in liquid ammonia giving a deep blue solution, which is paramagnetic. Reasons R : The deep blue solution is due to the formation of amide. In the light of the above statements, choose the correct answer from the options given below :

Recall the characteristic reactions and properties of alkali metals, especially their behavior in liquid ammonia.

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Ninja Strategy•Factual Recall of Solution Chemistry

A direct recall of the chemistry of alkali metals in liquid ammonia immediately identifies the true cause of the blue color and paramagnetism, allowing for quick elimination of options that misstate these facts.

Step 1: Evaluate Assertion A✦ Active

When metallic sodium (an alkali metal) dissolves in liquid ammonia, it forms ammoniated metal ions and ammoniated electrons. The reaction is represented as: Na(s)+(x+y)NH3(l)→[Na(NH3)x]++[e(NH3)y]−. The ammoniated electrons are responsible for the deep blue color and the paramagnetic nature of the solution. Therefore, Assertion A is true.

Step 2: Evaluate Reason R○ Expand

Reason R states that the deep blue solution is due to the formation of amide. This is incorrect. The deep blue color is due to the ammoniated electrons. Amide formation (NaNH2) occurs at higher concentrations or on prolonged standing, and it leads to a bronze color, not the initial deep blue color. Therefore, Reason R is false.

Step 3: Conclusion○ Expand

Based on the evaluation, Assertion A is true, but Reason R is false. This corresponds to option (3).

💡 Teacher's Secret Hint

Remember the distinction between the initial dissolution products and the products of subsequent reactions in liquid ammonia.

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