Which of the following is a physical change? 

The Correct answer is: 2) Glowing of a Pt wire when heated

Key Points

• Burning of a Mg wire in air:
  • This statement is incorrect.
  • When magnesium wire is burned in air, it reacts with oxygen to form magnesium oxide (MgO). This is a chemical change as new substances are formed, and it is irreversible.
  • Chemical changes involve the formation of new substances and changes in the chemical properties of the matter.
• Glowing of a Pt wire when heated:
  • This statement is correct.
  • When platinum wire is heated, it glows due to the increase in temperature. This is a physical change as there is no new substance formed, and the change is reversible.
  • Physical changes involve changes in the state or appearance of matter without changing its chemical composition.
• Electrolysis of acidulated water:
  • This statement is incorrect.
  • Electrolysis of acidulated water results in the decomposition of water into hydrogen and oxygen gases. This is a chemical change as new substances (hydrogen and oxygen) are formed.
  • Chemical changes involve breaking and forming of chemical bonds, resulting in different substances.
• Passing carbon dioxide through lime water:
  • This statement is incorrect.
  • When carbon dioxide is passed through lime water (calcium hydroxide solution), it forms calcium carbonate, which turns the lime water milky. This is a chemical change as a new substance (calcium carbonate) is formed.
  • Chemical changes result in the production of new substances with different properties from the original substances.

Additional Information

• Physical Changes:
  • Physical changes are usually reversible changes that do not involve the formation of new substances.
  • Examples include changes in state (melting, freezing, condensation) and changes in appearance or shape.
• Chemical Changes:
  • Chemical changes result in the formation of one or more new substances with different chemical and physical properties.
  • These changes are often irreversible and involve changes in the chemical composition of the substances involved.
• Indicators of Chemical Changes:
  • Formation of a precipitate, change in color, evolution of gas, and change in temperature are common indicators of chemical changes.