Matter & Mixtures — Set 1

Correct Answer: A. Distilled water

• **Pure substance** = Distilled water consists only of water molecules with a fixed composition. • **Single component** — Water has uniform properties throughout, unlike mixtures. • 💡 Wrong-option analysis: B: Air is a mixture of gases; C: Brass is a metal alloy mixture; D: Milk contains suspended particles.

Correct Answer: A. Homogeneous

• **Homogeneous mixture** = Sugar solution has uniform composition throughout with dissolved molecules at molecular level. • **Invisible particles** — The sugar particles are so small they cannot be seen, even under a microscope. • 💡 Wrong-option analysis: B: Heterogeneous mixtures show visible distinct phases; C: Colloids have particle size between solutions and suspensions; D: Suspensions have visible particles that settle.

Correct Answer: C. Solid

• **Solid structure** = Solids have definite shape and volume due to strong intermolecular forces between tightly packed particles. • **Fixed positions** — Particles vibrate in place but cannot move freely like in other states. • 💡 Wrong-option analysis: A: Liquids have definite volume but take the shape of their container; B: Plasma has neither definite shape nor volume; D: Gases have neither definite shape nor volume.

Correct Answer: B. Sublimation

• **Sublimation process** = Substance transitions from solid to gas without passing through the liquid phase. • **Common examples** — Dry ice and naphthalene balls sublime when exposed to heat. • 💡 Wrong-option analysis: A: Condensation is gas converting to liquid; C: Evaporation is liquid converting to gas; D: Deposition is gas converting directly to solid.

Correct Answer: A. Chemical bond formation

• **Chemical bonds** = A compound forms when two or more elements combine chemically in a fixed ratio with strong bonds. • **Fixed composition** — Compounds always have the same ratio of elements regardless of their source. • 💡 Wrong-option analysis: B: Compounds have fixed composition, not variable; C: Compounds require chemical methods to separate components; D: Component properties change when forming a compound.

Correct Answer: D. Alloy

• **Alloy definition** = A homogeneous mixture of two or more metals or a metal and a nonmetal combined together. • **Enhanced properties** — Alloys are created to improve properties like strength, corrosion resistance, or durability. • 💡 Wrong-option analysis: A: Isotopes are atoms of the same element with different neutrons; B: Monomers are single molecules; C: Polymers are long chain molecules.

Correct Answer: C. Dispersed phase

• **Dispersed phase** = The particles distributed throughout a colloidal system, ranging from 1 to 1000 nanometers. • **Suspended particles** — These particles remain suspended in the continuous medium rather than settling down. • 💡 Wrong-option analysis: A: Solute dissolves completely in a solution; B: Solvent is the substance that dissolves the solute; D: Dispersion medium is the continuous phase surrounding dispersed particles.

Correct Answer: D. Filtration after dissolving in water

• **Solubility difference** = Salt dissolves in water while sand remains insoluble, allowing separation by filtration. • **Two-step process** — First filter to separate sand, then evaporate water to recover salt. • 💡 Wrong-option analysis: A: Magnetic separation works only for magnetic materials; B: Simple distillation cannot separate both components; C: Fractional crystallization requires different solubilities in specific solvents.

Correct Answer: D. Rusting of iron

• **Rusting reaction** = Iron reacts with oxygen to form a new substance, iron oxide, making it a chemical change. • **Irreversible process** — The new substance cannot easily be converted back to iron metal. • 💡 Wrong-option analysis: A: Dissolving sugar is physical; B: Melting ice is physical state change; C: Boiling water is physical state change.

Correct Answer: A. Diffusion

• **Diffusion process** = Spontaneous mixing of particles until uniform concentration is achieved throughout. • **Driven by kinetic energy** — Particle motion is random but overall movement is from high to low concentration. • 💡 Wrong-option analysis: B: Sedimentation is settling of heavier particles; C: Effusion is gas escaping through a small hole; D: Osmosis is water movement through a semipermeable membrane.