Both soap and detergent are some type of salts. What is the difference between them? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water? List two problems that arise due to the use of detergents instead of soaps.

(A) Soaps are $Na^+$ or $K^+$ salts of long-chain carboxylic acids.
Detergents are ammonium or sulphonate salts of long-chain hydrocarbons.
Cleansing action of soap: $A$ soap molecule has two parts: a hydrophilic (water-loving) ionic head and a hydrophobic (water-repelling) hydrocarbon tail. The tail attaches to oily dirt,while the head remains in water. This forms a structure called a $micelle$. When rinsed,the $micelle$ is washed away,carrying the dirt with it.
Soaps do not form lather in hard water because they react with $Ca^{2+}$ and $Mg^{2+}$ ions present in hard water to form an insoluble precipitate known as $scum$.
Problems due to the use of detergents:
$1$. Most detergents are non-biodegradable,leading to water and soil pollution.
$2$. They can cause skin irritation or allergic reactions in some individuals.