Which of the following statements is not correct?

Question

Thermal stability order of Group 1 hydroxides is:

Answer 1

To determine which statement is incorrect, let's analyze each option based on the properties of Beryllium (Be) and Magnesium (Mg):

Statement: Be and Mg give characteristic colour to the flame.
This statement is incorrect. Typically, elements in the s-block of the periodic table give colored flames due to the excitation of electrons. However, Be and Mg are exceptions. They do not impart any characteristic color to the flame. This is because the energy required to excite Be and Mg's electrons to higher energy levels does not correspond to the visible spectrum, making the flame appear colorless.
Statement: Be and Mg have high ionisation energy.
This statement is correct. Both beryllium and magnesium have relatively high ionisation energies compared to other s-block elements. This is because both have fully filled s-orbitals, which are stable and thus require more energy to remove an electron.
Statement: Sulphates of Be and Mg are readily soluble in water.
This is also correct, although it may seem counterintuitive given general trends in group 2 elements. BeSO₄ is very soluble in water due to its strong covalent character, while MgSO₄ is moderately soluble. However, when compared to heavier alkaline earth metal sulfates, it is more soluble.
Statement: All are correct.
This statement is not correct because, as explained above, the first statement is incorrect.

Based on this analysis, the correct answer is that the statement "Be and Mg give characteristic colour to the flame" is not correct.

Answer 2

To determine which statement is incorrect, let's analyze each option based on the properties of Beryllium (Be) and Magnesium (Mg):

Statement: Be and Mg give characteristic colour to the flame.
This statement is incorrect. Typically, elements in the s-block of the periodic table give colored flames due to the excitation of electrons. However, Be and Mg are exceptions. They do not impart any characteristic color to the flame. This is because the energy required to excite Be and Mg's electrons to higher energy levels does not correspond to the visible spectrum, making the flame appear colorless.
Statement: Be and Mg have high ionisation energy.
This statement is correct. Both beryllium and magnesium have relatively high ionisation energies compared to other s-block elements. This is because both have fully filled s-orbitals, which are stable and thus require more energy to remove an electron.
Statement: Sulphates of Be and Mg are readily soluble in water.
This is also correct, although it may seem counterintuitive given general trends in group 2 elements. BeSO₄ is very soluble in water due to its strong covalent character, while MgSO₄ is moderately soluble. However, when compared to heavier alkaline earth metal sulfates, it is more soluble.
Statement: All are correct.
This statement is not correct because, as explained above, the first statement is incorrect.

Based on this analysis, the correct answer is that the statement "Be and Mg give characteristic colour to the flame" is not correct.

The Correct Option is A