Q 01/05

What is oxygen's atomic number?

A) 6

B) 4

C) 2

D) 8

Answer · why

D) 8

Its symbol is O and it belongs to the chalcogen group of the periodic table.

Q 02/05

Roughly what fraction of Earth's atmosphere is oxygen gas, by volume?

A) About 50%

B) About 78%

C) About 8%

D) About 21%

Answer · why

D) About 21%

Nitrogen makes up most of the rest; the oxygen figure has swung a great deal over geological time.

Q 03/05

Oxygen is the most abundant element in which part of the Earth?

A) The core

B) The crust

C) The mantle's iron

D) The atmosphere

Answer · why

B) The crust

It makes up 49.2% of the crust by mass, locked in oxides such as silica and iron oxide.

Q 04/05

Oxygen ranks where in abundance in the universe?

A) Third

B) Fifth

C) Second

D) First

Answer · why

A) Third

Only hydrogen and helium are more common; about 0.9% of the Sun's mass is oxygen.

Q 05/05

What is the chemical formula of ozone?

A) O6

B) O4

C) O5

D) O3

Answer · why

D) O3

This reactive allotrope absorbs UVB and UVC in the stratosphere but is a corrosive pollutant at ground level.