JEE Main 2023 · 25 January · evening · Single correct · +4 / −1
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : The alkali metals and their salts impart characteristic colour to reducing flame.
Reason R : Alkali metals can be detected using flame tests.
In the light of the above statements, choose the most appropriate answer from the options given below :
- (a) A is not correct but R is correct
- (b) A is correct but R is not correct
- (c) Both A and R are correct and R is the correct explanation of A
- (d) Both A and R are correct but R is NOT the correct explanation of A
Answer and solution
Answer (a) A is not correct but R is correct
Solution
Chemistry ma’am · 4 steps
Read every word of A: the colour shows up in the oxidising flame, not the reducing flame.
- Where colour comes from. The heat of the flame excites the loosely held outer ns¹ electron to a higher energy level. When it falls back, the energy comes out as visible light of a wavelength typical of that metal.
- Check Assertion A. This colour is seen in the oxidising flame, the hot, non-luminous outer part of the burner flame. A says reducing flame, so Assertion A is not correct.
- Check Reason R. Each alkali metal gives its own colour: Li crimson red, Na yellow, K violet, Rb red-violet, Cs blue. Because the colours are distinct, a flame test can detect these metals, so Reason R is correct.
- So. A is false and R is true, which is option (a).
The idea to keep. In assertion-reason questions, test each statement on its own first, word by word. One swapped word, like reducing for oxidising, is enough to make a statement false.
Answer from the NTA final answer key. Solution by PrepWiser.