Priestley was an 18th century scientist who made many important contributions including discovering oxygen gas and debunking the long-held belief that air was an elementary substance. He invented carbonated water and identified several chemical compounds. While known for discovering oxygen, Priestley wrote extensively on electricity and other scientific topics as well.

1. &

3. -The invisible gaseous substance surrounding the earth, a mixture mainly of
oxygen and nitrogen.
– Air in its liquid state, intensely cold and bluish, obtained by cooling and
compression.
-Rainfall made sufficiently acidic by atmospheric pollution that it causes
environmental harm, typically to forests and lakes. The main cause is the industrial
burning of coal and other fossil fuels, the waste gases from which contain sulfur and
nitrogen oxides, which combine with atmospheric water to form acids
-A layer in the earth's stratosphere at an altitude of about 10 km (6.2
miles) containing a high concentration of ozone, which absorbs most of the
ultraviolet radiation reaching the earth from the sun.
-Each of two or more different physical forms in which an element can
exist. Graphite, charcoal, and diamond are all allotropes of carbon

4. Priestley (1733-1804) was hugely productive
in research and widely notorious in
philosophy. He invented carbonated water
and the rubber eraser, identified a dozen key
chemical compounds, and wrote one of the
first comprehensive treatises on electricity.
But the world recalls Priestley best as the
man who discovered oxygen, the active
ingredient in our planet's atmosphere. In the
process, he helped dethrone an idea that
dominated science for 23 uninterrupted
centuries: Few concepts "have laid firmer
hold upon the mind," he wrote, then that air
"is a simple elementary substance,
indestructible and unalterable."

6. 79%
20%
0.03% 5%
0.9%
0.002%
Composition by volume of clean air
Nitrogen 78-79%
Oxygen 20%
Carbon dioxide 0.03%
Water vapor 0-5%
Argon 0.9%
Neon and Helium 0.002%

7. The liquid nitrogen boils at the bottom of the
column. Gaseous nitrogen rises to the top,
where it is piped off and stored. Liquid oxygen
collects at the bottom of the column. The boiling
point of argon - the noble gas that forms 0.9%
of the air - is close to the boiling point of
oxygen, so a second fractionating column is
often used to separate the argon

12. is a rain or any other form of
precipitation that is unusually acidic, meaning that it
possesses elevated levels of hydrogen ions (low pH).

14. .

20. Once they reach the stratosphere, the sun’s
ultraviolet rays break down the
compound, thus releasing chlorine.This
resulting chlorine is what damages the
ozone in a repetitive process. In fact, one
chlorine atom will continue to destroy the
ozone for as long as two years.

22. Answer:
Since the banning of CFC in industry (Montreal Protocol, 1989),
ozone depletion has mostly stopped with some signs that levels are increasing.
Scientists believe that ozone will return to its pre-CFC level by about 2050.
Ways to Protect the Ozone Layer:
Minimize high altitude aircraft flights (oxygen reduction and water vapor deposition)
Minimize rocket flights (water vapor deposition)
Decrease / control releases of high temperature steam / moisture to the atmosphere
Eliminate production and release of known ozone depleting chemicals (such as CFCs
and HCFCs) where remotely possible. Subsidize production of safer alternatives where
possible.
Establish controls to assure that new compounds to be used in high volume, are
surveyed for effect on ozone.