For the following data, which solution is the most concentrated, that is, has the greatest mass of solute per millilitre of solution?

Introduction / Context:
Concentration of a solution expresses how much solute is present in a given quantity of solvent or solution. One simple way to compare concentrations is to look at the mass of solute per unit volume of solution, often in grams per millilitre. This question gives several combinations of mass and volume and asks you to determine which solution is the most concentrated based on mass per millilitre comparison.

Given Data / Assumptions:

• Option A: 6 grams of solute in 10 millilitres of solution.
• Option B: 20 point 5 grams of solute in 50 millilitres of solution.
• Option C: 30 grams of solute in 120 millilitres of solution.
• Option D: 2 point 6 grams of solute in 2 millilitres of solution.
• Option E: 10 grams of solute in 25 millilitres of solution.
• We compare concentration as mass of solute divided by volume of solution.

Concept / Approach:
To identify the most concentrated solution, we convert each description to grams of solute per millilitre of solution by dividing the mass by the volume. The solution with the largest grams per millilitre value is the most concentrated. There is no need to convert to other units, because all masses are in grams and all volumes in millilitres, so we can compare the ratios directly.

Step-by-Step Solution:
Step 1: For option A, concentration equals 6 divided by 10, which is 0 point 6 grams per millilitre. Step 2: For option B, concentration equals 20 point 5 divided by 50, which is approximately 0 point 41 grams per millilitre. Step 3: For option C, concentration equals 30 divided by 120, which is 0 point 25 grams per millilitre. Step 4: For option D, concentration equals 2 point 6 divided by 2, which is 1 point 3 grams per millilitre. Step 5: For option E, concentration equals 10 divided by 25, which is 0 point 4 grams per millilitre. Comparing all results, option D has the highest concentration at 1 point 3 grams per millilitre.

Verification / Alternative check:
As an alternative check, notice that in option D the mass of solute is already more than the mass in some other options, but the volume is much smaller. Intuitively, putting 2 point 6 grams into only 2 millilitres should give a thicker or more concentrated solution than placing 6 grams into 10 millilitres or 20 point 5 grams into 50 millilitres. The numerical calculations confirm this intuition, since 1 point 3 grams per millilitre is clearly larger than all other computed values.

Why Other Options Are Wrong:
Option A gives 0 point 6 grams per millilitre, which is less than 1 point 3 grams per millilitre.
Option B yields about 0 point 41 grams per millilitre, again lower than the value for option D.
Option C has only 0 point 25 grams per millilitre, the lowest concentration among the options considered.
Option E gives 0 point 4 grams per millilitre, which is still smaller than the concentration of option D.

Common Pitfalls:
A common mistake is to look only at the absolute mass of solute or only at the volume and not at the ratio. For example, some might think that 30 grams in 120 millilitres must be more concentrated than 2 point 6 grams in 2 millilitres simply because the mass is larger, ignoring the much larger volume. Always compare concentrations by dividing mass by volume. Writing down the ratios in decimal form, as done here, makes it clear which solution is most concentrated.

Final Answer:
The most concentrated solution is the one with 2 point 6 grams of solute in 2 millilitres of solution, corresponding to option D.