s-Block Elements — JEE Main · 2023 · 15 Apr 2023 · Shift 1 Question with Solution

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R :

Assertion (A) :

BeCl_{2}

and

MgCl_{2}

produce characteristic flame.

Reason (R) : The excitation energy is high in

BeCl_{2}

and

MgCl_{2}

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

(A)Both (A) and (R) are true but (R) is NOT the correct explanation of (A)
(B)(A) is false but (R) is true✓ Correct
(C)Both (A) and (R) are true and (R) is the correct explanation of (A)
(D)(A) is true but (R) is false.

Answer: (B)

Solution

A flame test gives colour only when the heat of the flame can promote valence electrons to higher levels, from which they fall back emitting visible light. Beryllium and magnesium hold their valence electrons very tightly, so their excitation energies are large and the energy of an ordinary flame is insufficient to excite them; as a result

BeC l_{2}

and

MgC l_{2}

impart no characteristic colour to a flame. The assertion that they produce a characteristic flame is therefore false, while the reason that their excitation energy is high is true.

JEE Main · 2023 · 15 Apr 2023 · Shift 1 · Single correct option

JEE Main · 2023 · 15 Apr 2023 · Shift 1 · s-Block Elements

Solution

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