Q28 / 180 · COMEDK 2023 (Evening Shift) · Chemistry
Choose the incorrect statement.
- AAlkali and Alkaline earth metals cannot be produced by chemical reduction methods.
- B$\mathrm{LiF}$ and $\mathrm{Li}_3 \mathrm{~N}$ are thermally stable compounds.
- Correct answerCn the vapour phase $\mathrm{BeCl}_2$ has a polymeric chain structure consisting of numerous $\mathrm{BeCl}_2$ units.
- DWhen equimolar aqueous solutions of $\mathrm{SrCl}_2, \mathrm{MgCl}_2$ and $\mathrm{BaCl}_2$ are taken and their $\mathrm{pH}$ is recorded, $\mathrm{BaCl}_2$ solution recorded the highest $\mathrm{pH}$.
Solution
Alkali and alkaline earth metals have very high negative standard electrode potentials, making them strong reducing agents. Therefore, they cannot be reduced by common chemical reducing agents like carbon or hydrogen, so the statement in (hIfp2) is correct.
Lithium has a high lattice energy due to the small size of the $\text{Li}^{+}$ ion. $\text{LiF}$ has a very high lattice energy, and $\text{Li}_{3}\text{N}$ is stable due to the high charge density of the nitride ion, making both thermally stable. Thus, (YPHJq) is correct.
In the vapour phase, $\text{BeCl}_{2}$ exists as a monomer or a dimer, not a polymeric chain. The polymeric chain structure is characteristic of the solid state. Therefore, the statement in (IiFKW) is incorrect.
The salts $\text{SrCl}_{2}$, $\text{MgCl}_{2}$, and $\text{BaCl}_{2}$ are salts of strong acids and strong bases, but they undergo slight hydrolysis depending on the polarizing power of the cation. $\text{Mg}^{2+}$ has the highest polarizing power, leading to more acidic character (lower pH), while $\text{Ba}^{2+}$ has the lowest polarizing power, resulting in a solution closest to neutral (highest pH). Thus, (C28mo) is correct.
Answer: n the vapour phase $\mathrm{BeCl}_2$ has a polymeric chain structure consisting of numerous $\mathrm{BeCl}_2$ units.
Lithium has a high lattice energy due to the small size of the $\text{Li}^{+}$ ion. $\text{LiF}$ has a very high lattice energy, and $\text{Li}_{3}\text{N}$ is stable due to the high charge density of the nitride ion, making both thermally stable. Thus, (YPHJq) is correct.
In the vapour phase, $\text{BeCl}_{2}$ exists as a monomer or a dimer, not a polymeric chain. The polymeric chain structure is characteristic of the solid state. Therefore, the statement in (IiFKW) is incorrect.
The salts $\text{SrCl}_{2}$, $\text{MgCl}_{2}$, and $\text{BaCl}_{2}$ are salts of strong acids and strong bases, but they undergo slight hydrolysis depending on the polarizing power of the cation. $\text{Mg}^{2+}$ has the highest polarizing power, leading to more acidic character (lower pH), while $\text{Ba}^{2+}$ has the lowest polarizing power, resulting in a solution closest to neutral (highest pH). Thus, (C28mo) is correct.
Answer: n the vapour phase $\mathrm{BeCl}_2$ has a polymeric chain structure consisting of numerous $\mathrm{BeCl}_2$ units.
Hence, the correct answer is option: 'C'.