Option 1: The oil and dirt gets collected in the centre of the micelle.

This statement is true. When soap is mixed with water, it forms structures called micelles. Inside these micelles, the hydrophobic tails of the soap molecules attract and surround oil and dirt particles, while the hydrophilic heads face outwards towards the water.

Option 2: Soap micelles scatter light.

This statement is true. Soap micelles are large enough to scatter light, which is why we can see the soap solution as cloudy or opaque.

Option 3: Soaps are ammonium salts of long chain carboxylic acids.

This statement is not true. Soaps are actually salts of sodium or potassium with long chain carboxylic acids, not ammonium salts.

Option 4: Soap forms insoluble precipitates with the calcium and magnesium ions in hard water.

This statement is true. Soap reacts with calcium and magnesium ions in hard water to form insoluble precipitates, which can cause a decrease in the cleansing ability of the soap.

In conclusion, the correct answer is option 3, as soaps are not ammonium salts of long chain carboxylic acids.