Is Matter Around us Pure? — Practice Quiz

Only (ii) shows Tyndall effect; (i) shows no scattering; (iii) shows scattering only when freshly prepared.

Step 1: Tyndall effect occurs only when particle size is in the colloidal range (1 nm to 1000 nm). Step 2: Copper sulphate solution (i) is a true solution — particles are less than 1 nm. They are too small to scatter light, so NO Tyndall effect. Step 3: Milk diluted in water (ii) is a colloid — fat droplets are in the colloidal size range. They scatter light, showing the Tyndall effect clearly. Step 4: Chalk powder in water (iii) is a suspension. When freshly prepared, large chalk particles scatter light. But after 10 minutes, the chalk settles down, the mixture becomes clearer, and scattering

Because its composition can be varied and it shows properties of its constituent metals.

Step 1: A compound has a fixed composition and completely new properties different from its constituents. Step 2: A mixture has variable composition and retains properties of its constituents. Step 3: Brass can be made with different percentages of copper and zinc (e.g., 60:40 or 70:30) — its composition is NOT fixed, so it is a mixture. Step 4: Brass also shows metallic properties like lustre and conductivity, which are properties of its constituent metals copper and zinc. Step 5: Even though alloys cannot be separated by simple physical methods, they are still mixtures because of variable co

26.47%

Step 1: Mass of solute (NaCl) = 36 g. Step 2: Mass of solvent (water) = 100 g. Step 3: Mass of solution = 36 + 100 = 136 g. Step 4: Mass by mass % = (Mass of solute / Mass of solution) × 100 = (36/136) × 100. Step 5: = 0.2647 × 100 = 26.47%. Option B (36%) is wrong because that would mean dividing 36 by 100 (treating solvent mass as solution mass). Option C (26%) is close but not precise — the exact answer requires proper calculation to get 26.47%. Option D (18%) has no mathematical basis for this calculation.

Different substances have the same solubility in a given solvent at the same temperature.

Step 1: A saturated solution is one in which no more solute can dissolve at a given temperature. Step 2: The question asks for the INCORRECT statement — so we look for the false one. Step 3: Option C states that different substances have the SAME solubility in a given solvent — this is INCORRECT. From Activity 2.3 in the chapter, we observe that salt and sugar or barium chloride dissolve in different amounts in the same volume of water, proving that different substances have DIFFERENT solubilities. Step 4: Option A is correct — adding more solvent (not changing temperature) allows more solute