An example of a complex salt is

The correct option is D

tetraamine copper (II) sulphate

Part 1 Explanation for the correct option

The correct option is D

Tetraamine copper (II) sulphate $\left[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4\right]{\mathrm{SO}}_4·{\mathrm{H}}_2\mathrm{O}.$

1. When exposed to air, the deep blue crystalline solid tends to hydrolyze and evolve (release) ammonia. It is water-soluble to a degree.
2. The presence of $[\mathrm{Cu}{\left({\mathrm{NH}}_3\right)}_4{]}^{2+}$ gives the Tetraammine copper(II) sulphate solution a stunning dark blue-violet colour.
3. The presence ${\mathrm{Cu}}^{2+}$ in a solution is frequently confirmed using the dark blue-violet colour as a positive test.

Part 2 Explanation for incorrect options

Option A.

Zinc sulphate $\left({\mathrm{ZnSO}}_4\right)$ is an inorganic compound and also a dietary supplement that's used to treat and prevent zinc deficiency in persons who are at high risk. Excessive supplementation can cause abdominal pain, vomiting, headaches, and tiredness, among other things.

Option B.

Sodium hydrogen sulphate $\left({\mathrm{NaHSO}}_4\right)$ common ingredient in toilet bowls and dishwasher cleansers. It can also be found in a wide variety of other products.

Option C.

Ferrous ammonium sulphate $({\mathrm{FeSO}}_4.{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4)$ is a crystalline solid with a pale green colour. The threat to the environment is the most serious danger. Immediate action should be done to prevent it from spreading to the environment. It has applications in medicine, chemistry, and metallurgy.

Therefore, tetraamine copper (II) sulphate is an example of a complex salt