Which of the following is an example of a pure substance?
A. Milk
B. Sea water
C. Air
D. Distilled water
Answer: Option D
Solution (By JKExamLibrary)
Distilled water is a pure compound (H₂O) with a fixed composition and distinct properties. Milk is a colloid of fat, protein, etc. Air is a homogeneous mixture of gases. Sea water is a solution of salts. Pure substances are either elements or compounds; mixtures contain two or more substances physically combined. Distillation removes dissolved salts and impurities.
Explanation:
Saponification: Fat/oil + NaOH → glycerol + sodium salt of fatty acid (soap). NaCl is used to precipitate soap from solution (salting out).
Explanation:
The mass of an atom is almost entirely concentrated in its tiny central nucleus. This is because the nucleus contains protons and neutrons, which are much heavier than the extranuclear electrons. Since electrons have negligible mass, R correctly explains why the mass is localized in the nucleus.
Explanation:
Boyle's law: P ∝ 1/V or PV = constant at constant T and n. So if volume increases, pressure decreases. This is because gas molecules have more space and hit the walls less frequently. An example is a syringe: pulling the plunger increases volume, decreases pressure.
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