Question

Which of the following ions forms a hydroxide that is highly soluble in water?

• A. ${\mathrm{K}}^{+}$
• B. ${\mathrm{Zn}}^{2+}$
• C. ${\mathrm{Ni}}^{2+}$
• D. ${\mathrm{Al}}^{+3}$

Answer 1

The correct option is A

${\mathrm{K}}^{+}$

Explanation for the correct option

A: ${\mathrm{K}}^{+}$

Alkali metals

• On the s-block of the periodic table, a group of chemical elements with related characteristics are known as the alkali metals.
• Alkali metals quickly lose their outermost electrons at standard pressure and temperature, generating cations with a charge of plus one.

Solubility of Alkali metal hydroxides

• The term "solubility" refers to a substance's capacity to dissolve in a solvent.
• In alkaline earth metal hydroxides, where the anion is more prevalent, the cationic radius will have an effect on the lattice enthalpy.
• The lattice enthalpy decreases significantly more than the hydration enthalpy with increasing ionic size, and solubility rises down the group.
• Potassium is a alkali metal.
• Hence, potassium ions (${\mathrm{K}}^{+}$) form potassium hydroxide $\left(\mathrm{KOH}\right)$ that is highly soluble in water.

Explanation for the incorrect options:

B. ${\mathrm{Zn}}^{2+}$

• The zinc hydroxide ($\mathrm{Zn}{\left(\mathrm{OH}\right)}_2$) is slightly soluble in water.

C. ${\mathrm{Ni}}^{2+}$

• The nickel hydroxide ($\mathrm{Ni}{\left(\mathrm{OH}\right)}_2$) is slightly soluble in water.

D. ${\mathrm{Al}}^{+3}$

• Hydroxides of Aluminum are insoluble in water.

Hence, the correct option is (A) ${\mathrm{K}}^{+}$.