Questions

The comma ( , ) is a punctuation mark in English which is most frequently used.

It is perhaps also the most abused and misused punctuation mark among all.

Neurons are the functional units of the nervous system in the body.

Convection is the mode of heat transfer which involves bulk motion of a fluid to transfer heat. Energy transfer by convection is primarily restricted to fluids. Fluids can be both liquids and gases.

A reflection.

A Disease which spreads by contact are Contagious.

Infectious diseases : These are caused by microscopic germs such as bacteria or viruses that get into the body and cause problems. Some but not all infectious diseases spread directly from one person to another. Infectious diseases that spread from person to person are said to be contagious. Some infections spread to people from an animal or insect, but are not contagious from another human. 

Contagious diseases such as the flu, colds, or strep throat spread from person to person in several ways. One way is through direct physical contact, like touching or kissing a person who has the infection. Another way is when an infectious microbe travels through the air after someone nearby sneezes or coughs.

Fatal Diseases : Diseases leading to failure or disaster.

Incurable Diseases : Diseases of a sick person not able to be cured.

Secondary pollutants include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight.

Whereas Primary pollutant are those pollutants that are directly emitted from their sources, like CO2, CO, SO2 as these gases are directly emitted form burning of fossil fuels.

Acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water, sulfuric acid etc.

Hence, Acidrain is a secondary air pollutant.

DNA fingerprinting is used to identify the parents, thieves and rapists.