Q4. Classify each as a gaseous, liquid or solid solution: (a) air; (b) vinegar, ethanoic acid in water; (c) an idealised single-phase 22-carat gold alloy with copper as its only added metal.
(a) Gaseous (nitrogen is the solvent). (b) Liquid. (c) Solid (types as in NCERT Table 1.1, page 2).
Q5. Which type of solution is camphor in nitrogen gas, and what is unusual about it?
A solid solute in a gaseous solvent, so a gaseous solution (NCERT Table 1.1, page 2). What is unusual is a solid dissolving in a gas: camphor sublimes, so its molecules pass into the nitrogen as vapour (reasoned).
Q6. Assertion: brass and bronze are solutions. Reason: they are homogeneous mixtures of metals. Are both true, and does the reason explain the assertion?
For the idealised single-phase brass and bronze meant by NCERT, both are true and the reason explains the assertion. As a universal statement about commercial brass or bronze it is too broad: alloy composition and cooling history can give several phases.
Q7. A 500 mL sample of water (density 1 kg L−1) contains 0.75 mg of fluoride ions. What is its concentration in ppm by mass, and is it the level NCERT says prevents tooth decay?
0.75 mg in 5 × 105 mg of water is 0.75 × 106/(5 × 105) = 1.5 ppm, the concentration at which NCERT says the tooth becomes mottled, against the 1 ppm that prevents tooth decay (NCERT page 1). Strictly, the risk depends on total exposure while teeth develop, not on a sharp 1.5 ppm switch (reasoned).
Q8. Why must an intravenous injection be made up in water with salts at particular concentrations?
NCERT’s answer: the salts must be at ionic concentrations that match blood plasma concentrations (NCERT page 1), so the injection is isotonic with the fluid in blood cells, like normal saline, 0.9% (mass/volume) sodium chloride (NCERT page 22). Strictly, its osmotic effect and chemical compatibility must suit blood; it need not copy every plasma ion (reasoned). The NCERT example illustrates concentration control, not a recipe for injection.