How many litres of pure acid are present in 8 litres of a 20% acid solution?

Introduction / Context:
This question deals with percentage concentration in a solution. A 20% acid solution means that 20% of the total volume is pure acid and the rest is typically some other substance such as water. This type of problem is very common in mixture and solution questions in quantitative aptitude, chemistry basics, and everyday reasoning about concentrations.

Given Data / Assumptions:

• Total volume of the solution = 8 litres.
• The solution is 20% acid by volume.
• We are asked to find the volume of pure acid in the solution.
• We assume the solution is homogeneous and that 20% concentration is measured by volume.

Concept / Approach:
To find the volume of pure acid, we simply take 20% of the total volume of the solution. In percentage terms, this is (20/100) times the total volume. Because the total volume is given as 8 litres, multiplying 8 by 0.2 or 20/100 gives the volume of acid. This is a direct and straightforward calculation involving percentages and unit consistency.

Step-by-Step Solution:
Step 1: Total volume of solution = 8 litres.Step 2: Concentration of acid in the solution = 20%.Step 3: Volume of pure acid = 20% of 8 litres.Step 4: Compute 20% of 8 = (20/100) * 8.Step 5: (20/100) * 8 = 0.2 * 8 = 1.6.Step 6: Therefore, the volume of pure acid is 1.6 litres.

Verification / Alternative check:
Another quick way to see this is to recognise that 10% of 8 litres is 0.8 litres. Therefore, 20% is twice that value, which is 1.6 litres. This mental math check matches our detailed calculation, confirming that 1.6 litres is correct. Since all operations are simple and there are no additional conditions or changes in concentration, the answer is unambiguous.

Why Other Options Are Wrong:
Option 1.4 litres corresponds to 17.5% of 8 litres, which is less than the given 20% concentration. Option 1.5 litres corresponds to 18.75% of 8 litres, again not matching 20%. Option 1.7 litres is slightly higher than 20% of 8 litres and would represent about 21.25%. Option 1.2 litres corresponds to 15% of 8 litres. Only 1.6 litres exactly corresponds to 20% of 8 litres, so the other options do not fit the problem statement.

Common Pitfalls:
Some learners confuse percentage of volume with percentage points and may mistakenly compute 20% of 10 litres or misread the total volume. Others might misplace the decimal when multiplying by 0.2. To avoid mistakes, clearly identify the base quantity (8 litres), convert the percentage to a fraction (20/100), and perform the multiplication carefully. Quick mental checks like using 10% and doubling it can also help verify the result.

Final Answer:
There are 1.6 litres of pure acid in the 8-litre solution.