Solution:
Concept: When copper sulphate is heated up to 230 degrees C temperature, it loses a molecule of water to form anhydrous copper sulphate. The first statement is therefore true.When copper sulphate reacts with ammonium hydroxide, it forms a copper complex in which the complex cation has (II) ion surrounded by four ammonia ligands. As we can see, a coordinate compound is formed as one of the products, which makes this statement also a correct one.
A white precipitate of silver chloride is produced when silver nitrate and hydrochloric acid interact. Nitric acid is the byproduct. This is also a true statement.
Potassium chloride and mercuric iodide are produced when mercuric chloride and potassium iodide combine. There is an exchange of ions between two reactants and therefore this reaction is an example of a double displacement reaction and not a displacement reaction. Therefore, the last statement given is untrue.
Hence, the correct answer is option 3.