Q5 / 150 · MHT CET 2026 (13 April Shift 2) · Chemistry
Identify the elements of alkali metals and alkaline earth metals respectively having highest 1st ionization enthalpy.
- A$\text{K}$ and $\text{Ca}$
- Correct answerB$\text{Li}$ and $\text{Be}$
- C$\text{Rb}$ and $\text{Ba}$
- D$\text{K}$ and $\text{Sr}$
Solution
Ionization enthalpy decreases down a group in the periodic table due to an increase in atomic size and shielding effect.
Among alkali metals (Group 1), Lithium ($\text{Li}$) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy.
Among alkaline earth metals (Group 2), Beryllium ($\text{Be}$) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy.
Therefore, the elements with the highest first ionization enthalpy are $\text{Li}$ and $\text{Be}$ respectively.
Answer: $\text{Li}$ and $\text{Be}$
Among alkali metals (Group 1), Lithium ($\text{Li}$) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy.
Among alkaline earth metals (Group 2), Beryllium ($\text{Be}$) is at the top of the group and has the smallest atomic size, hence it has the highest first ionization enthalpy.
Therefore, the elements with the highest first ionization enthalpy are $\text{Li}$ and $\text{Be}$ respectively.
Answer: $\text{Li}$ and $\text{Be}$
Hence, the correct answer is option: 'B'.