Which one of the following processes involves chemical reaction?

The correct answer is Burning of magnesium ribbon in air.

Key Points

• Burning of magnesium ribbon in air:
  • This process involves a chemical reaction.
  • When magnesium ribbon burns in the presence of oxygen (from the air), it undergoes a chemical reaction to form magnesium oxide.
  • The reaction can be represented as:
    • 2Mg + O₂ → 2MgO
  • During this process, the chemical composition of the magnesium changes, indicating a chemical reaction.

Additional Information

• Evaporation of petrol:
  • Evaporation is a physical process, not a chemical reaction.
  • It involves the conversion of a liquid into a vapor without any change in the chemical composition of the substance.
  • In the case of petrol, it is the evaporation of the liquid hydrocarbons.
• Dissolution of salt in water:
  • ​Dissolving salt in water is also a physical process.
  • It is a dissolution or solvation process where the salt crystals break down into ions in the water, but there is no chemical reaction involved.
• Storing of oxygen gas under pressure in a gas cylinder:
  • ​Storing oxygen gas under pressure is a physical process related to the compression and storage of gases.
  • It does not involve any chemical reaction; it's merely a change in the physical state of the gas.