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
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
- A.Both A and R are correct and R is the correct explanation of A
- B.Both A and R are correct but R is NOT the correct explanation of A
- C.A is correct but R is not correct
- D.A is not correct but R is correct
Show answer and solution
Correct option: A
Solution
The standard reduction potential (E°) depends on the overall energetics: ionization energy, atomization enthalpy, and hydration energy. Be²⁺, due to its exceptionally small size, has a very large hydration energy (around -2494 kJ/mol), which makes the reduction process less favorable compared to larger alkaline earth metal ions. However, Be also has a relatively large atomization enthalpy, which further opposes the dissolution/reduction process. The net effect of these competing factors — large hydration energy being outweighed by the high ionization energy and atomization enthalpy — results in Be having a less negative (less favorable) reduction potential compared to Mg, Ca, Sr, and Ba. Thus R correctly explains the balance of thermodynamic terms that gives Be its less negative E° value, making both A and R correct with R being the proper explanation of A.
[JEE Main 2023 · 24 Jan · Shift 2]