A collective noun is a noun that can be singular in form whilst referring to a group of people or things. Collective nouns are sometimes confused with mass nouns.ome collective nouns can stand alone, such as Britain has an army, but if the collective noun army is used to mean something other than an organized military force, you can say things like an army of women or an army of ants, and even an army of one.
Rainwater is slightly acidic because the CO2 in the atmosphere is soluble in water (the water in the air). When in solution CO2 forms a weak acid (Carbonic acid) which makes pure rainwater a weak acid. 1 person found this useful.
Some contamination might also happen at the ozone layer. Pure rain water is slightly acidic at a pH level of 5.6. Contaminated rainwater can have a pH level of between 4 and 5. In most areas of the U.S., the pH level of rainwater has been ranging from 4-5. The contamination level in the environment causes these unfavorable pH levels.