Basic Chemistry (Elements, Compounds, Reactions) MCQs

1. The smallest unit of an element that retains its chemical properties is called:
(A) Molecule
(B) Atom
(C) Compound
(D) Ion

2. Which of the following is a compound?
(A) Oxygen (O₂)
(B) Hydrogen (H₂)
(C) Water (H₂O)
(D) Nitrogen (N₂)

3. The atomic number of an element represents the number of:
(A) Neutrons
(B) Protons
(C) Electrons
(D) Nucleons

4. Which subatomic particle carries a negative charge?
(A) Proton
(B) Neutron
(C) Electron
(D) Nucleus

5. Which of the following is an example of a chemical change?
(A) Melting of ice
(B) Rusting of iron
(C) Breaking of glass
(D) Boiling of water

6. The element with the highest atomic number in the periodic table is:
(A) Uranium
(B) Oxygen
(C) Hydrogen
(D) Oganesson

7. What is the chemical formula of table salt?
(A) NaCl
(B) KCl
(C) HCl
(D) CaCl₂

8. Which of the following is NOT a noble gas?
(A) Helium
(B) Argon
(C) Neon
(D) Oxygen

9. What type of bond is formed when two atoms share electrons?
(A) Ionic bond
(B) Covalent bond
(C) Metallic bond
(D) Hydrogen bond

10. What is the pH of a neutral solution?
(A) 0
(B) 7
(C) 14
(D) 10

11. The reaction between an acid and a base is called:
(A) Oxidation
(B) Neutralization
(C) Reduction
(D) Precipitation

12. Which gas is produced when metals react with acids?
(A) Oxygen
(B) Hydrogen
(C) Carbon dioxide
(D) Nitrogen

13. What is the chemical symbol of gold?
(A) Ag
(B) Au
(C) Pb
(D) Hg

14. The most abundant element in the Earth’s crust is:
(A) Carbon
(B) Oxygen
(C) Silicon
(D) Iron

15. Which of the following is an example of an exothermic reaction?
(A) Melting of ice
(B) Boiling of water
(C) Burning of wood
(D) Evaporation of alcohol

16. Which type of reaction involves the loss of electrons?
(A) Reduction
(B) Oxidation
(C) Neutralization
(D) Hydrolysis

17. The periodic table is arranged based on the:
(A) Atomic mass
(B) Atomic number
(C) Number of neutrons
(D) Electron configuration

18. A solution with a pH less than 7 is:
(A) Neutral
(B) Acidic
(C) Basic
(D) Alkaline

19. What happens to the rate of a chemical reaction when temperature increases?
(A) It decreases
(B) It remains unchanged
(C) It increases
(D) It stops

20. Which element is essential for respiration?
(A) Nitrogen
(B) Oxygen
(C) Carbon
(D) Hydrogen