Industrial Chemistry — Set 2

Correct Answer: D. CO and H2

• **Water gas** = Produced by passing steam over red-hot coke at 1000°C. • **Fuel value** — CO and H₂ both combust to provide energy equivalent to natural gas. • 💡 Wrong-option analysis: A: CO₂ is end product of combustion, not produced here; B: N₂ not produced from steam-coke reaction; C: CH₄ requires different process.

Correct Answer: D. Tungsten

• **Tungsten (W)** = Has melting point of 3422°C, highest among all metals. • **White-hot glow** — Can be heated to 2700°C safely without melting or oxidizing rapidly. • 💡 Wrong-option analysis: A: Copper melts at 1083°C, too low for this use; B: Nichrome melts at 1400°C, insufficient; C: Silver oxidizes quickly at high heat.

Correct Answer: C. Sodium thiosulfate

• **Sodium thiosulfate (Na₂S₂O₃)** = Dissolves unexposed silver halides, making photographic image permanent. • **'Hypo' process** — Chemical bath that removes light-sensitive material to prevent further exposure. • 💡 Wrong-option analysis: A: Potassium nitrate is oxidizer, not solvent for silver halides; B: Sodium chloride is salt, doesn't dissolve Ag halides; D: Silver bromide is light-sensitive, must be removed.

Correct Answer: D. Sulfuric acid

• **Sulfuric acid (H₂SO₄)** = Serves as electrolyte, enabling ion flow between lead plates during charging/discharging. • **Lead-acid chemistry** — Provides necessary conductivity while reacting with PbO₂ and Pb electrodes. • 💡 Wrong-option analysis: A: HCl would corrode positive plate; B: Phosphoric acid lacks conductivity; C: HNO₃ oxidizes lead plates, causing damage.

Correct Answer: C. Mercury

• **Cinnabar (HgS)** = Red mineral, primary source of mercury, found in volcanic regions worldwide. • **Roasting and condensation** — Ore heated in air produces mercury vapor that condenses to liquid metal. • 💡 Wrong-option analysis: A: Zinc extracted from sphalerite (ZnS); B: Lead from galena (PbS); D: Copper from chalcopyrite (CuFeS₂).

Correct Answer: A. Chlorine

• **Chlorine gas (Cl₂)** = Bleaching powder contains hypochlorite, releasing Cl₂ when acidified. • **Bleaching and disinfection** — Cl₂ oxidizes chromophores (colored compounds), destroying stains and bacteria. • 💡 Wrong-option analysis: B: CO₂ doesn't react with bleaching powder; C: O₂ too weak oxidizer for bleaching; D: H₂ doesn't produce from this reaction.

Correct Answer: C. Methane

• **Methane (CH₄)** = Comprises 75-90% of natural gas, simplest hydrocarbon. • **Clean combustion** — Burns with highest heat output among alkanes, producing only CO₂ and H₂O. • 💡 Wrong-option analysis: A: Butane (C₄H₁₀) separates as LPG, much heavier; B: Propane (C₃H₈) also liquefied separately; D: Ethane (C₂H₆) present but minor.

Correct Answer: B. Galvanization

• **Galvanization** = Zinc coating acts as sacrificial anode, oxidizing instead of iron. • **Hot-dip process** — Iron immersed in molten zinc at 840°C, forming zinc-iron alloy layer. • 💡 Wrong-option analysis: A: Smelting is ore reduction process, not coating; C: Vulcanization applies to rubber, not metals; D: Annealing is heat treatment for hardness.

Correct Answer: A. Graphite

• **Graphite (C)** = Carbon allotrope mixed with clay in varying proportions (higher clay = harder pencil). • **Misnomer** — Despite being called 'lead', pencils contain no actual lead metal, only graphite. • 💡 Wrong-option analysis: B: Lead is toxic, never used in pencils; C: Coal contains impurities, too abrasive; D: Charcoal burns away, can't write consistently.

Correct Answer: D. Ammonia

• **Ammonia (NH₃)** = High latent heat of vaporization (1371 kJ/kg) makes it excellent refrigerant. • **Industrial use** — Cost-effective and environmentally friendly compared to synthetic refrigerants. • 💡 Wrong-option analysis: A: Argon doesn't undergo phase change easily; B: CO₂ less efficient, used only in niche applications; C: N₂ extremely low boiling point (-196°C).