Cette série est proposée dans sa langue d’origine.

1. Notion: Atomic structure

   1. The atomic number of an element is the number of

   AneutronsBprotonsCelectrons and neutronsDprotons and neutrons
   Correction

   B. protons

   • The atomic number is the number of protons in the nucleus.
   • Protons and neutrons together give the mass number.

2. Notion: Periodic table

   2. How does the reactivity of Group 1 metals change going down the group?

   AIt decreasesBIt increasesCIt stays the sameDIt increases then decreases
   Correction

   B. It increases

   • Going down Group 1, the outer electron is further from the nucleus.
   • It is lost more easily, so the metals become more reactive.

3. Notion: Chemical tests

   3. Which gas relights a glowing splint?

   AHydrogenBCarbon dioxideCOxygenDChlorine
   Correction

   C. Oxygen

   • Oxygen relights a glowing splint.
   • Hydrogen gives a squeaky pop with a lit splint.

4. Notion: Acids and alkalis

   4. What is the pH of a neutral solution?

   A0B1C7D14
   Correction

   C. 7

   • pH 7 is neutral.
   • Below 7 is acidic, above 7 is alkaline.

5. Notion: Quantitative chemistry

   5. Calculate the relative formula mass of CO₂. (Ar: C = 12, O = 16)

   A28B32C44D56
   Correction

   C. 44

   • Mr = 12 + (2 × 16).
   • 12 + 32 = 44.

6. Notion: Bonding

   6. What type of bonding is found in sodium chloride?

   ACovalentBIonicCMetallicDHydrogen
   Correction

   B. Ionic

   • Sodium is a metal and chlorine is a non-metal.
   • Sodium transfers an electron to chlorine, forming Na⁺ and Cl⁻ ions: ionic bonding.

7. Notion: Chemical tests

   7. Which is the test for carbon dioxide?

   AIt turns limewater milkyBIt relights a glowing splintCIt bleaches damp litmus paperDIt gives a squeaky pop
   Correction

   A. It turns limewater milky

   • Carbon dioxide turns limewater milky (cloudy).
   • Chlorine bleaches damp litmus paper.

8. Notion: Acids and alkalis

   8. What are the products when an acid reacts with a metal carbonate?

   ASalt and hydrogenBSalt and waterCSalt, water and carbon dioxideDMetal oxide and water
   Correction

   C. Salt, water and carbon dioxide

   • Acid + metal carbonate gives a salt, water and carbon dioxide.
   • Acid + metal gives a salt and hydrogen.

9. Notion: Electrolysis

   9. During the electrolysis of molten lead bromide, what forms at the cathode?

   ABromineBLeadCHydrogenDOxygen
   Correction

   B. Lead

   • Positive lead ions (Pb²⁺) are attracted to the negative cathode.
   • They gain electrons and form lead metal.

10. Notion: Energy changes

    10. In an exothermic reaction, the temperature of the surroundings

    AdecreasesBincreasesCstays the sameDfalls to zero
    Correction

    B. increases

    • Exothermic reactions transfer energy to the surroundings.
    • So the temperature of the surroundings increases.