8. Which compound has nitrogen and hydrogen?
– a) CO₂
– b) NaCl
– c) NH₃ ✅
– d) H₂O
9. The unit of atomic mass is:
– a) gram
– b) kg
– c) u ✅
– d) mg
10. What is the formula for calcium oxide?
– a) CaO₂
– b) Ca₂O
– c) CaO ✅
– d) Ca(OH)₂
11. Sodium chloride is made of:
– a) Na and O
– b) Na and Cl ✅
– c) Cl and H
– d) Na and N
12. What is the valency of calcium?
– a) 1
– b) 2 ✅
– c) 3
– d) 4
13. Which of these is a chemical formula?
– a) HCl ✅
– b) Water
– c) Hydrogen
– d) Atom
14. What is the atomic mass of oxygen?
– a) 8
– b) 10
– c) 16 ✅
– d) 18
15. What does a molecule consist of?
– a) Protons
– b) Two or more atoms ✅
– c) Electrons only
– d) Neutrons only
True or False
1. Dalton believed atoms can be divided. → False
2. Water is always made of hydrogen and oxygen in a 2:1 ratio by atoms. → True
3. The law of conservation of mass says mass can be created. → False
4. All atoms have the same mass. → False
5. Atoms are very large and visible. → False
6. A molecule of oxygen contains two atoms. → True
7. Sodium chloride is made of ions. → True
8. Chemical formulas represent compounds. → True
9. The atomic mass of hydrogen is 12 u. → False
10. Valency shows how an atom can combine. → True
11. CaCl₂ contains one calcium atom and two chlorine atoms. → True
12. An ion is always neutral. → False
13. The molecular mass of CO₂ is 44 u. → True
14. Polyatomic ions contain only one atom. → False
15. The formula of ammonium sulphate is (NH₄)₂SO₄. → True
