Which of the following substances sublimes on heating?
A. Sodium chloride
B. Iodine
C. Sugar
D. Copper
Answer: Option B
Solution (By JKExamLibrary)
Iodine directly converts from solid to violet vapor on gentle heating (sublimation). NaCl melts; sugar decomposes; copper melts at high temperature. Other sublimable substances: camphor, naphthalene, dry ice.
Explanation:
The number of half-lives elapsed is 30 days / 10 days = 3. The fraction remaining is (1/2)ⁿ, where n is the number of half-lives. So, (1/2)³ = 1/8. After 10 days: 1/2; after 20 days: 1/4; after 30 days: 1/8 of the original amount remains.
Explanation:
Natural gas (methane) is often found above petroleum deposits, trapped under cap rock. It burns cleaner than coal and oil, producing less CO₂, no SO₂, and minimal particulates. Coal (including lignite) contains more impurities. Peat is an early stage of coal. Natural gas is transported via pipelines or as LNG.
Explanation:
Sodium carbonate is a salt of strong base (NaOH) and weak acid (H₂CO₃). On hydrolysis, it gives OH⁻ ions: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻, making the solution basic. pH ~11. It turns red litmus blue. It is used for softening hard water and in detergents. NaHCO₃ solution is also mildly basic. Salts of strong acid + strong base are neutral (NaCl). Salts of weak base + strong acid are acidic (NH₄Cl).
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