JEE Main 2023 · 15 April · morning · 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) : BeCl₂ and MgCl₂ produce characteristic flame
Reason (R) : The excitation energy is high in BeCl₂ and MgCl₂
In the light of the above statements, choose the correct answer from the options given below :
- (a) (A) is true but (R) is false
- (b) Both (A) and (R) are true and (R) is the correct explanation of (A)
- (c) (A) is false but (R) is true
- (d) Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
Answer and solution
Answer (c) (A) is false but (R) is true
Solution
Chemistry ma’am · 4 steps
Be and Mg hold their electrons too tightly for a Bunsen flame to excite them, so no colour.
- How flame colour works. The flame's heat lifts an outer electron to a higher level. When it falls back, it gives out light, and we see a colour only if that light is in the visible range.
- Be and Mg. Be and Mg are small atoms, so their outer electrons are held very strongly. Exciting them needs more energy than a Bunsen flame can give, so their salts give no characteristic flame colour. This makes the Assertion false.
- Check the Reason. The Reason says the excitation energy is high in BeCl₂ and MgCl₂. That is a correct fact, so R is true. It is in fact the reason these salts show no colour.
- So. A is false and R is true, which is option (c).
The idea to keep. In Group 2, only Ca (brick red), Sr (crimson) and Ba (apple green) colour the flame. Be and Mg need too much excitation energy, so they show no flame colour.
Answer from the NTA final answer key. Solution by PrepWiser.