1. The smallest unit of an element that retains its chemical properties is called:
(A) Atom
(B) Molecule
(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) Boiling of water
(C) Breaking of glass
(D) Rusting of iron
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) Precipitation
(C) Reduction
(D) Neutralization
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) Au
(B) Ag
(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) Hydrogen
(C) Carbon
(D) Oxygen