In the following question, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices:

Assertion: Fe³⁺ can be used for coagulation of As₂S₃ sol.

Reason : Fe³⁺ reacts with As₂S₃ to give Fe₂S₃.

Assertion is true but the reason is false.

The correct answer is option 3. Assertion is true but the reason is false.

Assertion: \(Fe^{3+}\) can be used for coagulation of \(As_2S_3\) sol.

The assertion is correct because \(Fe^{3+}\) ions can indeed be used to coagulate \(As_2S_3\) sol (a colloidal solution of arsenic sulfide). Coagulation involves destabilizing the colloidal particles so that they come together and form larger aggregates, ultimately leading to the separation of the sol into a precipitate and a clear liquid.

Reason : \(Fe^{3+}\) reacts with As₂S₃ to give \(Fe_2S_3\).

The reason provided is incorrect. \(Fe^{3+}\) ions do not react with \(As_2S_3\) to form \(Fe_2S_3\). Instead, they react with As2S3 to form an insoluble compound called FeAsS, also known as arsenopyrite or arsenic pyrite. This reaction leads to the formation of solid particles of FeAsS, which then coagulate with the As2S3 sol particles, contributing to the overall coagulation process.

So, while the assertion is true, the reason is false, making option 3 the correct choice.