O-Level Combined Science — Chemistry 1 — Questions and Answers
Question 1: What is the chemical formula for water?
- HO
- H₂O₂
- H₂O (Correct answer)
- OH₂
Correct answer: H₂O
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?
- Ionic bond
- Metallic bond
- Covalent bond (Correct answer)
- Hydrogen bond
Correct answer: Covalent bond
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?
- 0
- 7 (Correct answer)
- 14
- 1
Correct answer: 7
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?
- Oxygen
- Hydrogen
- Carbon dioxide (Correct answer)
- Nitrogen
Correct answer: Carbon dioxide
Acid + metal carbonate → salt + water + carbon dioxide. The CO₂ produced turns limewater milky.
Question 5: What is the relative atomic mass of carbon?
- 6
- 12 (Correct answer)
- 14
- 16
Correct answer: 12
The relative atomic mass of carbon is 12 (specifically, the isotope carbon-12 is the standard reference).
Question 6: Which type of reaction releases heat energy to the surroundings?
- Endothermic
- Photosynthesis
- Exothermic (Correct answer)
- Electrolysis
Correct answer: Exothermic
Exothermic reactions release heat energy to the surroundings, causing the temperature of the surroundings to rise.
O-Level Combined Science — Chemistry 1
What is the chemical formula for water?