Question

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:
Assertion (A): B_eCl₂ and MgCl₂ produce characteristic flame. 
Reason (R) : The excitation energy is high in B_eCl₂ and MgCl₂ 
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
• C. Both (A) and (R) are true and (R) is the correct explanation of (A)
• D. (A) is true but (R) is false.

Hint:

Flame tests are effective for metals with low ionization energies, like alkali metals

Answer 1

The Correct Option is D

To determine whether the assertion and reason are true and whether the reason correctly explains the assertion, we must understand the chemistry behind the fluorescence of beryllium chloride (BeCl₂) and magnesium chloride (MgCl₂), and the concept of excitation energy.

1. Assertion (A): BeCl₂ and MgCl₂ produce characteristic flame.
   • The production of a characteristic flame color is related to the ability of the metal ions to become excited when heated and then emit light as they return to a lower energy state. In the case of many alkaline earth metals, like calcium (Ca) or strontium (Sr), this is indeed observable as these metals tend to display noticeable colors.
   • However, BeCl₂ and MgCl₂ are exceptions among their group. Beryllium and magnesium do not typically produce characteristic flame colors because their ionization energies are much higher, meaning they require significantly more energy to get excited compared to other alkali or alkaline earth metals. Thus, BeCl₂ and MgCl₂ actually do not produce characteristic visible colors readily. Hence, Assertion (A) is false.
2.  Reason (R): The excitation energy is high in BeCl₂ and MgCl₂.
   • This statement accurately describes the situation for BeCl₂ and MgCl₂. The high excitation energy means these compounds or their elements do not easily impart color to a flame. Therefore, Reason (R) is true.

Conclusion: The assertion provided that BeCl₂ and MgCl₂ produce characteristic flame is not true, while the reason stating the high excitation energy is accurate. Therefore, the correct answer is: (A) is false but (R) is true.