If 0.2g of a salt is required to saturate 200$cm^{3}$ of water at room temperature, what is the solubility of the salt?

Analyze the question: We're told that 0.2 g of salt saturates 200 cm³ of water. We need the solubility in g/dm³, which means the mass of salt that saturates 1 dm³ (1000 cm³) of water.

Concept: Solubility is the amount of solute (here in grams) that dissolves in a given volume of solvent to form a saturated solution. In g dm⁻³, we express it per 1000 cm³.

Solution:

• 200 cm³ of water dissolves 0.2 g
• 1000 cm³ of water dissolves x g

x = (0.2 × 1000) / 200 = 200 / 200 = 1.0 g dm⁻³

Check: 1000 cm³ is 5 times 200 cm³, so the mass is 5 times 0.2 g = 1.0 g. This matches the calculation.

Answer: The solubility is 1.0 g dm⁻³, which is option B.

Tip: For solubility conversions, always scale to 1000 cm³ (1 dm³). Multiply the mass by 1000/volume. A common mistake is to divide by 5 instead of multiplying by 5, which gives the wrong option A or C.