Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : The energy required to form Mg²⁺ from Mg is much higher than that required to produce Mg⁺
Reason R: Mg²⁺ is small ion and carry more charge than Mg⁺
In the light of the above statements, choose the correct answer from the options given below.

Solution

Chemistry ma’am · 4 steps

The second electron comes off an ion that is already positive and smaller, so it costs about twice as much.

1. Check Assertion A. Making Mg⁺ needs only the first ionisation enthalpy, about 738 kJ mol⁻¹. Making Mg²⁺ needs the first and the second together, so the total is much larger. A is true.

   Mg → Mg²⁺: Δᵢ H₁ + Δᵢ H₂ ≈ 738 + 1451 = 2189 kJ mol⁻¹

2. Check Reason R. Mg²⁺ has lost its whole 3s shell, so it is much smaller than Mg⁺. It also carries a 2+ charge against 1+. R is true.
3. Link R to A. Once one electron is gone, the same 12 protons pull on fewer electrons. The ion shrinks and the remaining electron is held more tightly, and it must be pulled away from a positive ion. That stronger hold, from smaller size and higher charge, is why the second step costs so much more.
4. So. Both statements are correct, and the smaller size and higher charge of the ion explain the extra energy. The answer is (c).

The idea to keep. Each electron you remove leaves a smaller, more positive ion, so the next one is held tighter. Successive ionisation enthalpies always increase: Δᵢ H₁ < Δᵢ H₂ < Δᵢ H₃.

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