The correct answer is option 4: 1, 2, and 3.

Let`s dissect each statement to better understand why they are correct:

1. Simple aliphatic carboxylic acids are soluble in water: This statement is true because simple aliphatic carboxylic acids, such as acetic acid, have a polar carboxyl group (-COOH) that can form hydrogen bonds with water molecules. Consequently, they are soluble in water.

2. Higher carboxylic acids are practically insoluble in water: This statement is also correct. As the size of the hydrocarbon chain in a carboxylic acid increases, the hydrophobic effect becomes dominant, making these compounds less soluble in water.

3. The acidity of a carboxylic acid depends on the number of carbon atoms present in the hydrocarbon chain: This statement is true. The presence of more carbon atoms in the hydrocarbon chain increases the stability of the carboxylate ion that forms when a carboxylic acid donates a proton. Consequently, carboxylic acids with longer hydrocarbon chains have a higher degree of acidity.

Therefore, all three statements are correct, leading to the correct answer being option 4.