Chemical Reaction

1. When magnesium ribbon burns in the air, what is the ash-like substance that is formed?

• A) Magnesium sulphate
• B) Magnesium carbonate
• C) Magnesium chloride
• D) Magnesium oxide

2. What is the fundamental principle that necessitates the balancing of a chemical equation?

• A) Energy must be conserved in all reactions.
• B) The products must always be gaseous.
• C) Atoms cannot be created or destroyed, only rearranged.
• D) The reactants must be in equal amounts by mass.

3. In a chemical equation, where are the formulas or symbols of the products written?

• A) On the left of the arrow sign
• B) Above the arrow sign
• C) On the right of the arrow sign
• D) Below the arrow sign

4. Which reaction described in the text is an example of an endothermic process, where heat is absorbed from the surroundings?

• A) Burning a candle
• B) The reaction between lime and vinegar
• C) The reaction between baking soda and lemon juice
• D) The combustion of a magnesium ribbon

5. What is the short expression of an element called?

• A) Formula
• B) Symbol
• C) Radical
• D) Compound

6. According to the text, what is the valency of oxygen?

• A) 1
• B) 2
• C) 3
• D) 4

7. Why does the blue solution of copper sulphate turn light green when iron powder is added to it?

• A) Because the iron powder itself is green.
• B) Because the reaction releases green-colored gas.
• C) Because the newly formed ferrous sulphate has a light green color.
• D) Because the pure copper that forms is green.