JEE Main · 2023 · 24 Jan 2023 · Shift 2 · s-Block Elements

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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 : Beryllium has less negative value of reduction potential compared to the other alkaline earth metals.
Reason R : Beryllium has large hydration energy due to small size of but relatively large value of atomization enthalpy.
In the light of the above statements, choose the most appropriate answer from the options given below.
  1. (A)A is correct but R is not correct
  2. (B)Both A and R are correct and R is the correct explanation of A .✓ Correct
  3. (C)A is not correct but R is correct
  4. (D)Both A and R are correct and R is NOT the correct explanation of A .

Answer: (B)

Solution

Beryllium does show a less negative reduction potential than the other alkaline earth metals, so the assertion holds. Its reduction potential is fixed by the balance of atomisation enthalpy, ionisation enthalpy and hydration enthalpy; although the small ion gives a very large hydration enthalpy that would push the potential more negative, the unusually high atomisation enthalpy works the other way and dominates, leaving the potential less negative. Since this interplay is just what the reason describes, the reason is true and correctly explains the assertion.

JEE Main · 2023 · 24 Jan 2023 · Shift 2 · Single correct option

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