O-Level Combined Science — Chemistry

Question 1

What is the chemical formula for water?

Accepted Answer

H₂O

Answer

Water has the chemical formula H₂O — two hydrogen atoms bonded to one oxygen atom.

Question 2

Which type of bond involves the sharing of electrons?

Accepted Answer

Covalent bond

Answer

Covalent bonds are formed by the sharing of electron pairs between atoms, typically between non-metal atoms.

Question 3

What is the pH of a neutral solution?

Accepted Answer

7

Answer

A neutral solution has a pH of 7. Below 7 is acidic; above 7 is alkaline/basic.

Question 4

Which gas is produced when an acid reacts with a metal carbonate?

Accepted Answer

Carbon dioxide

Answer

Acid + metal carbonate → salt + water + carbon dioxide. The CO₂ produced turns limewater milky.

Question 5

What is the relative atomic mass of carbon?

Accepted Answer

12

Answer

The relative atomic mass of carbon is 12 (specifically, the isotope carbon-12 is the standard reference).

GCE O-Level Practice Test