Answer all the questions below.
1. Which of the following is the simplest form of matter that cannot be broken down by chemical means?
a) Compound
b) Element
c) Mixture
d) Molecule
2. The smallest particle of an element that retains its properties is called—
a) Atom
b) Proton
c) Molecule
d) Ion
3. Which subatomic particle has a negative charge?
a) Proton
b) Electron
c) Neutron
d) Nucleus
4. The nucleus of an atom contains—
a) Protons only
b) Electrons and neutrons
c) Protons and neutrons
d) Electrons only
5. Which of the following is a physical change?
a) Burning wood
b) Rusting iron
c) Melting ice
d) Baking bread
6. A molecule of oxygen (O₂) is—
a) A compound
b) A mixture
c) An element
d) An atom
7. Which subatomic particle determines the identity of an element?
a) Electron
b) Neutron
c) Proton
d) Isotope
8. Which of these is an element?
a) Water
b) Salt
c) Oxygen
d) Carbon dioxide
9. The number of protons in an atom is called—
a) Mass number
b) Atomic number
c) Valence number
d) Isotopic number
10. Which statement best describes a physical change?
a) New substances are always formed
b) It is always irreversible
c) It involves change in state or form
d) It produces heat and light
11. Which of the following is NOT a physical property?
a) Density
b) Melting point
c) Reactivity with acid
d) Solubility
12. When a solid changes directly into gas, the process is called—
a) Melting
b) Sublimation
c) Condensation
d) Evaporation
13. Which subatomic particle has no charge?
a) Proton
b) Electron
c) Neutron
d) Isotope
14. Which of these is a mixture?
a) Oxygen gas
b) Carbon dioxide
c) Table salt
d) Air
15. The sum of protons and neutrons in an atom is called—
a) Atomic number
b) Mass number
c) Valence number
d) Nucleon number
16. Which of the following represents a chemical change?
a) Dissolving sugar in water
b) Freezing water
c) Burning a candle
d) Cutting paper
17. An atom with 6 protons belongs to—
a) Oxygen
b) Carbon
c) Nitrogen
d) Sulfur
18. What holds electrons in orbit around the nucleus?
a) Gravity
b) Magnetic force
c) Electric force of attraction
d) Neutron repulsion
19. The lightest particle among these is—
a) Proton
b) Electron
c) Neutron
d) Nucleus
20. Which of these changes is reversible?
a) Rusting
b) Melting wax
c) Cooking rice
d) Burning paper
21. Which of the following best defines an isotope?
a) Atoms with the same number of protons but different neutrons
b) Atoms with different protons and electrons
c) Atoms with no neutrons
d) Atoms with extra electrons
22. Which is NOT an element?
a) Hydrogen
b) Helium
c) Water
d) Gold
23. When water boils, what type of change occurs?
a) Physical change
b) Chemical change
c) Nuclear change
d) Permanent change
24. Which scientist proposed the indivisible nature of the atom?
a) Rutherford
b) Dalton
c) Bohr
d) Thomson
25. Which of these is a compound?
a) Nitrogen
b) Hydrogen
c) Sodium chloride
d) Iron
