I need past jamb questions on chemistry

Here are some past JAMB chemistry questions:

1. Which of the following is a noble gas? A. Oxygen B. Nitrogen C. Helium D. Hydrogen

   Answer: C. Helium

   Explanation: Noble gases are elements in Group 18 of the periodic table. They are known for their inertness. Helium (He) is the first element in this group.

2. What is the pH of a neutral solution at 25°C? A. 0 B. 7 C. 14 D. 1

   Answer: B. 7

   Explanation: A neutral solution has an equal concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻). The pH scale measures the acidity or alkalinity of a solution. A pH of 7 is considered neutral.

3. The process by which a liquid changes into a gas is called: A. Condensation B. Evaporation C. Freezing D. Melting

   Answer: B. Evaporation

   Explanation: Evaporation is the process where a substance in a liquid state changes to a gaseous state due to an increase in temperature and/or pressure. Condensation is the opposite (gas to liquid). Freezing is liquid to solid, and melting is solid to liquid.

4. What is the chemical formula for sodium chloride? A. NaClO₃ B. Na₂CO₃ C. NaCl D. NaHCO₃

   Answer: C. NaCl

   Explanation: Sodium chloride is an ionic compound formed between sodium (Na⁺) and chloride (Cl⁻) ions. The charges balance, resulting in the formula NaCl.

5. Which law states that for a fixed amount of gas at constant temperature, the volume is inversely proportional to the pressure? A. Charles's Law B. Boyle's Law C. Gay-Lussac's Law D. Avogadro's Law

   Answer: B. Boyle's Law

   Explanation: Boyle's Law describes the relationship between pressure and volume of a gas when the temperature and the amount of gas are kept constant. It is mathematically expressed as P₁V₁ = P₂V₂.