Potassium tetrahydroxidozincate (II) can be represented by which of the following formula?

$K_2[Zn(OH)_4]$

The correct answer is Option (2) → $K_2[Zn(OH)_4]$

The name “tetrahydroxidozincate(II)” gives complete information about the complex.

• Central metal ion: $\text{Zn}^{2+}$
• Ligands: $4$ hydroxide ions ($\text{OH}^-$)
• “Tetra” $= 4$
• “Hydroxido” $= \text{OH}^-$ ligand
• “Zincate” $=$ negatively charged complex
• Oxidation state of Zn $= +2$

Now calculate charge on the complex:

$\text{Zn}^{2+} = +2$

$4\text{ OH}^- = -4$

Net charge $= +2 - 4 = -2$

So the complex ion formed is:

$[\text{Zn}(\text{OH})_4]^{2-}$

To balance $-2$ charge, we need $2$ potassium ions ($\text{K}^+$).

Therefore, the correct formula is:

$\text{K}_2[\text{Zn}(\text{OH})_4]$

Option 1: $\text{K}_3[\text{Zn}(\text{OH})_4]$

$3 \, \text{K}^+$ ions give $+3$ charge.

Complex has $-2$ charge.

Charges do not balance.

Hence incorrect.

Option 2: $\text{K}_2[\text{Zn}(\text{OH})_4]$

$2 \, \text{K}^+$ gives $+2$ charge.

Complex has $-2$ charge.

Charges balance perfectly.

Correct coordination structure.

Hence correct answer.

Option 3: $[K_2(OH)_4]Zn$

This shows potassium inside the coordination sphere.

In coordination compounds:

• Metal ion must be inside bracket

• Ligands are attached to central metal

Here Zn is outside bracket, which is incorrect representation.

Hence incorrect.

Option 4: $[K(OH)_4]_2Zn$

Potassium cannot act as central metal in such complexes.

Also Zn is outside bracket, which is structurally wrong.

Hence incorrect.