Matter & Mixtures — Set 4

Correct Answer: D. Law of Conservation of Mass

• **Conservation of Mass law** = Proposed by Antoine Lavoisier, states total mass remains constant during chemical reactions. • **Equal mass principle** — Mass of reactants always equals mass of products in a closed system. • 💡 Wrong-option analysis: A: Avogadro's law relates volume to number of molecules; B: Law of Definite Proportions deals with element ratios; C: Law of Multiple Proportions deals with varying ratios of elements.

Correct Answer: D. Silicon

• **Silicon properties** = Exhibits both metallic and non-metallic properties, making it a true metalloid. • **Semiconductor element** — Used extensively in electronics and computer industries due to its semi-conducting nature. • 💡 Wrong-option analysis: A: Aluminum is a metal; B: Iron is a metal; C: Copper is a metal.

Correct Answer: A. Solid carbon dioxide

• **Dry ice composition** = The solid form of carbon dioxide, known for not melting into a liquid state. • **Direct sublimation** — Converts directly from solid to gas at room temperature, releasing CO₂ gas. • 💡 Wrong-option analysis: B: Frozen water is regular ice; C: Frozen methane is different compound; D: Solid nitrogen exists at much lower temperature.

Correct Answer: D. 1:8

• **1 to 8 ratio** = According to the Law of Definite Proportions, water maintains hydrogen and oxygen in 1:8 mass ratio. • **Constant composition** — This ratio remains the same regardless of water's source or purity. • 💡 Wrong-option analysis: A: 2:1 is incorrect mass ratio; B: 1:2 is reverse of correct ratio; C: 8:1 is inverted ratio.

Correct Answer: C. Oxygen

• **Oxygen abundance** = Most abundant element in Earth's crust, comprising nearly 46% of its mass. • **Primary form** — Found mainly in silicate minerals and oxide compounds throughout the crust. • 💡 Wrong-option analysis: A: Iron comprises about 5% of crust; B: Silicon is second at about 28%; D: Aluminum is third at about 8%.

Correct Answer: D. Kelvin

• **Kelvin scale** = The primary unit of temperature in the International System of Units (SI). • **Absolute scale** — Starts at absolute zero where all thermal motion theoretically stops. • 💡 Wrong-option analysis: A: Celsius is not SI standard though widely used; B: Joule measures energy; C: Fahrenheit is a non-standard scale.

Correct Answer: A. It has a fixed melting point

• **Fixed melting point** = Pure chemical compounds have a sharp and constant melting point unique to that substance. • **Composition consistency** — The melting point does not vary as long as the compound remains pure. • 💡 Wrong-option analysis: B: Compounds are distinct from mixtures; C: Compound properties are consistent, not variable; D: Constituents require chemical, not physical separation.

Correct Answer: D. Concentration

• **Concentration definition** = Measures how much solute is dissolved in a specific volume of solvent or solution. • **Various expressions** — Can be expressed as mass percentage, molarity, or molality depending on context. • 💡 Wrong-option analysis: A: Viscosity is thickness of liquid; B: Solubility is maximum amount that can dissolve; C: Density is mass per unit volume.

Correct Answer: D. Carbon dioxide

• **Carbon dioxide use** = Dissolved under high pressure into soft drinks to create carbonation and fizz. • **Preservation function** — Also acts as a mild preservative extending shelf life. • 💡 Wrong-option analysis: A: Nitrogen is used in some applications but not for fizz; B: Hydrogen is flammable and unsuitable; C: Oxygen would cause oxidation.

Correct Answer: C. A homogeneous mixture

• **Brass composition** = An alloy consisting of copper and zinc mixed uniformly at the atomic level. • **Homogeneous nature** — Appears as a single phase with uniform properties throughout the material. • 💡 Wrong-option analysis: A: Brass is not visibly heterogeneous; B: Brass is a mixture, not chemically bonded; D: Brass contains multiple elements.