Q 01/05

What is the chemical formula for water?

A) H2O

B) CO2

C) O2

D) H2O2

Answer · why

A) H2O

Each molecule has two hydrogen atoms bonded to one oxygen atom.

Q 02/05

About what fraction of Earth's surface is covered by water?

A) 50%

B) 30%

C) 71%

D) 90%

Answer · why

C) 71%

Seas and oceans hold most of that water.

Q 03/05

Water is often called the 'universal' what?

A) Element

B) Solvent

C) Acid

D) Catalyst

Answer · why

B) Solvent

Its polarity lets it dissolve a huge range of substances.

Q 04/05

Unusually, water's solid form is what compared with its liquid form?

A) More dense

B) The same density

C) Twice as dense

D) Less dense

Answer · why

D) Less dense

That is why ice floats; water expands by about 9% when it freezes.

Q 05/05

At standard pressure, water boils at what temperature?

A) 50 degrees C

B) 212 degrees C

C) 80 degrees C

D) 100 degrees C

Answer · why

D) 100 degrees C

That is a high boiling point for such a small molecule, thanks to hydrogen bonding.