Which of the following is an example of a pure substance?
A. Distilled water
B. Milk
C. Air
D. Sea water
Answer: Option A
Solution (By JKSSB Mock Tests)
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:
DAP (diammonium phosphate) contains N (18%) and P₂O₅ (46%). Urea only N; MOP (muriate of potash) only K; SSP only P. NPK mixtures provide all three.
Explanation:
Bauxite (Al₂O₃·2H₂O) is the principal ore of aluminium. Magnetite (Fe₃O₄) and haematite (Fe₂O₃) are iron ores. Zinc blende is ZnS. Bauxite is refined by Bayer's process to obtain pure alumina, which is then electrolyzed in cryolite.
Explanation:
Pure rainwater naturally has pH about 5.6 because CO₂ from air dissolves and forms carbonic acid. This is not considered acid rain. Acid rain has pH below 5.0 (due to SO₂ and NOₓ).
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