21. The primary use of nitrogen in the industry is:

a) As a refrigerant
b) In explosives
c) In fertilizers
d) In welding
Answer: c) In fertilizers

22. The compound used in the treatment of water and as a disinfectant is:

a) Nitric acid
b) Sulfur dioxide
c) Chlorine
d) Phosphoric acid
Answer: b) Sulfur dioxide

23. The Group VA element that is used as a doping agent in semiconductors is:

a) Nitrogen
b) Phosphorus
c) Arsenic
d) Antimony
Answer: d) Antimony

24. The primary source of phosphorus for agricultural use is:

a) Phosphate rock
b) Nitrogen gas
c) Sulfur dioxide
d) Ammonium chloride
Answer: a) Phosphate rock

25. The common form of nitrogen found in the Earth’s atmosphere is:

a) N₂
b) NO
c) NO₂
d) NH₃
Answer: a) N₂

26. The oxide of sulfur that is a major contributor to acid rain is:

a) SO
b) SO₂
c) SO₃
d) H₂SO₄
Answer: b) SO₂

27. The Group VIA element that is essential for respiration and is a major component of the Earth’s crust is:

a) Oxygen
b) Sulfur
c) Selenium
d) Tellurium
Answer: a) Oxygen

28. The most reactive form of phosphorus is:

a) White phosphorus
b) Red phosphorus
c) Black phosphorus
d) Purple phosphorus
Answer: a) White phosphorus

29. The compound of phosphorus that is used in the production of matches is:

a) Phosphoric acid
b) Phosphorus trichloride
c) Red phosphorus
d) White phosphorus
Answer: d) White phosphorus

30. The main use of nitric acid is:

a) In the production of fertilizers
b) In the manufacture of explosives
c) As a cleaning agent
d) As a refrigerant
Answer: b) In the manufacture of explosives