Detergents having highly branched hydrocarbon chains cause pollution in rivers. The reason being that side chains stop bacteria from attacking and breaking the chains.

Thus, lesser the branching more is the biodegradability i.e., detergents with long straight hydrocarbon chains are more easily degraded than those having branched hydrocarbon chains.

Since, unbranched (i.e., straight) chains are more prone to attack by bacteria, therefore, in most of the detergents used these days, the branching is kept to be minimum, so that the detergents become easily biodegradable.

Soaps are biodegradable while detergents containing branched hydrocarbon chains are quite stable, i.e., they are not degraded by the action of microorganism and therefore it cause water pollution in rivers and other water ways.

Analgesics reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbances of nervous system.

These are classified in two groups

(i) Non-narcotic analgesics These are non-addictive analgesics e.g., aspirin.

(ii) Narcotic analgesics Morphine is an example of narcotic analgesics.

Noradrenaline is a neuro-transmitter which plays an crucial role in mood changes. If any person has low level of noradrenaline, then the message transfer process becomes slow and the person feeling of depression.

Antiseptics and disinfectants both are antimicrobials. Antiseptics prevent or destroy development or inhibit the pathogenic action of microbes. They are safe to be applied on living tissues.

On the other hand, disinfectants also kill microorganisms but are not safe to be applied on living tissues. They are generally applied on non-living objects such as drains, toilets, floors and living rooms infected with bacteria and disease carrying germs.