A mixture of sodium chloride and iron filings
Explanation
Matter is classified into pure substances and mixtures. Mixtures are further categorized based on the uniformity of their composition:
- Homogeneous Mixtures: These have a uniform composition throughout the bulk. The components are not distinct and form a single phase (e.g., true solutions).
- Heterogeneous Mixtures: These have a non-uniform composition. The components remain physically distinct, and there are visible boundaries of separation between them.
Option Analysis
- A solution of sugar in water: Incorrect. A solution of sugar in water is a homogeneous mixture. The sugar molecules dissolve and distribute evenly within the water, resulting in a uniform composition.
- A solution of common salt in water: Incorrect. A solution of common salt in water is a homogeneous mixture. The salt particles are uniformly distributed, and the solution appears clear and consistent throughout.
- A mixture of sodium chloride and iron filings: Correct. A mixture of sodium chloride and iron filings is a heterogeneous mixture. The two solids do not blend to form a uniform phase; the salt crystals and iron filings remain distinct and can be seen separately. They can also be separated easily by physical methods, such as using a magnet to remove the iron.
- A solution of copper sulphate in water: Incorrect. A solution of copper sulphate in water is a homogeneous mixture. It forms a clear solution where the solute is uniformly distributed within the solvent.
Key Takeaway
Heterogeneous mixtures are characterized by non-uniform composition and visible boundaries between components (e.g., sand and salt), whereas homogeneous mixtures have a uniform composition throughout (e.g., salt solutions).