Matter & Mixtures — Set 5

Correct Answer: B. Evaporation

• **Evaporation process** = Surface phenomenon where liquid turns into vapor at any temperature below the boiling point. • **Cooling effect** — High-energy particles escape from surface, causing the remaining liquid to cool down. • 💡 Wrong-option analysis: A: Condensation is vapor converting to liquid; C: Sublimation is solid directly to gas; D: Boiling occurs at boiling point temperature.

Correct Answer: B. Nitrogen

• **Nitrogen abundance** = Makes up approximately 78% of Earth's atmosphere by volume. • **Biological importance** — Relatively inert but essential as it is fixed into compounds needed by living organisms. • 💡 Wrong-option analysis: A: Carbon dioxide comprises only 0.04%; C: Oxygen is second at about 21%; D: Argon is about 0.93%.

Correct Answer: C. Liquids and gases

• **Fluids definition** = Substances that can flow and take the shape of their container, which includes both liquids and gases. • **Particle mobility** — Both states allow particles to move relative to each other unlike solids. • 💡 Wrong-option analysis: A: Liquids alone are not the only fluids; B: Solids do not have fluidity; D: Gases alone are incomplete answer.

Correct Answer: D. Milk of magnesia

• **Sol definition** = A colloid where solid particles are dispersed in a liquid medium. • **Example system** — Milk of magnesia contains magnesium hydroxide solid suspended in water, making it a clear sol. • 💡 Wrong-option analysis: A: Milk is an emulsion (liquid in liquid); B: Cheese is a gel (solid in solid); C: Fog is an aerosol (liquid in gas).

Correct Answer: C. Aurum

• **Aurum designation** = The symbol for gold is 'Au', which is derived from its Latin name 'Aurum'. • **Symbol origin** — Chemical symbols often come from Latin or Greek names for historical elements. • 💡 Wrong-option analysis: A: Ferrum is Latin for iron; B: Kalium is Latin for potassium; D: Argentum is Latin for silver.

Correct Answer: C. Diamond

• **Diamond purity** = A pure form of the element carbon arranged in a crystal structure. • **Pure carbon substance** — Contains only carbon atoms bonded in a crystalline lattice arrangement. • 💡 Wrong-option analysis: A: Glass is a silicon compound mixture; B: Air is a mixture of gases; D: Steel is an alloy of iron and carbon.

Correct Answer: D. Brownian motion

• **Brownian motion** = Random movement of particles resulting from collisions with molecules of the surrounding medium. • **Observable phenomenon** — First observed by Robert Brown while studying pollen grains in water under a microscope. • 💡 Wrong-option analysis: A: Diffusion is directional particle movement; B: Osmosis is water movement through membrane; C: Tyndall effect is light scattering.

Correct Answer: C. Oxygen gas

• **Oxygen gas** = Possesses the largest intermolecular spaces among all listed options. • **Weak attractions** — Gas particles experience minimal attractive forces and are far apart from each other. • 💡 Wrong-option analysis: A: Ice has tightly packed molecules; B: Water has closer packing than ice; D: Iron rod has extremely tight atomic packing.

Correct Answer: D. 18 grams

• **18 gram molar mass** = Water (H₂O) has molar mass calculated from two hydrogen (1 amu each) plus one oxygen (16 amu). • **Calculation basis** — Total mass equals 1 + 1 + 16 = 18 grams per mole. • 💡 Wrong-option analysis: A: 2 grams would be for dihydrogen; B: 10 grams is not the sum; C: 16 grams is only oxygen's mass.

Correct Answer: A. Milk

• **Emulsion definition** = A colloid where both the dispersed phase and the medium are liquids. • **Milk structure** — Oil droplets dispersed in water, stabilized by proteins like casein to prevent separation. • 💡 Wrong-option analysis: B: Smoke is an aerosol (solid in gas); C: Shaving cream is a foam (gas in liquid); D: Cloud is an aerosol (water droplets in air).