All of the following are sources of air pollution, except
a) chlorofluorocarbons (cfcs).
b) heavy metals such as mercury.
c) nitrogen oxides from automotive exhaust.
d) small particles of smoke and dust in smog.

The correct answer is B) Heavy metals such as mercury.

Explanation:

Heavy metals such as mercury or lead are denser than regular metals, this causes it is common for these metals to be found in the surface of Earth rather than in the air or atmosphere. Indeed, mercury and other similar metals are extracted from the Earth's crust and then used for different purposes. As a result of this, mercury ends up in the surface of Earth or in water sources which causes soil or water pollution. This means mercury is not a common source of air pollution; on the opposite other such as CFCs, nitrogen oxides and smog remain in the air and therefore are sources of air pollution.

me and my friend did 2

ans.

dna fingerprinting is defined as a process that determines the dna characteristics of an individual. these dna characteristics are unique among individuals as their fingerprints, so it is known as dna fingerprinting.

steps of dna fingerprinting includes extraction of dna from sample, amplification of dna, restriction digestion of amplified dna, and then analysis of dna by gel electrophoresis, respectively.

thus, the next step performed by the scientist is 'to cut the amplified dna (obtained by polymerase chain reaction) by restriction enzymes that cleave the dna into fragments and their analysis.'