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 Be²⁺ but relatively large value of atomization enthalpy
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Follow Be from solid metal to aqueous ion: atomizing it costs more than hydration can pay back.

1. Check Assertion A. E°(Be²⁺/Be) is about -1.97 V. For Mg it is -2.36 V, and Ca, Sr and Ba are near -2.9 V. So Be has the least negative value in the group, and A is correct.
2. Split into steps. Turning the solid metal into the aqueous ion takes three stages: atomize the solid, remove two electrons, then hydrate the ion. A more negative E° means this whole change is more favourable.

   M(s) →(Δₐ H) M(g) →(IE₁ + IE₂) M²⁺(g) →(Δ_(hyd) H) M²⁺(aq)

3. Check Reason R. Be²⁺ is very small, so its hydration enthalpy is large and negative, which helps. But metallic bonding in Be is strong, so its atomization enthalpy is also large, and this cost outweighs the hydration gain. R is correct, and it is exactly the balance that explains A.
4. So. Both statements are correct and R is the correct explanation of A, which is option (b).

The idea to keep. To compare E° values, add up the energy steps: atomization, ionization and hydration. A large hydration gain cannot help if getting gaseous ions costs even more.

Answer from the NTA final answer key. Solution by PrepWiser.