• The strength of an acid can be measured using the concept of molarity. Molarity is defined as the number of moles of solute present in one litre of the solution.
• Let’s denote the strength of the 20% sulphuric acid as M1 and the strength of the 100% pure sulphuric acid as M2.
• The total volume of the mixture is 10 litres.
• The amount of sulphuric acid in the mixture is 5 litres of 20% acid, which is equal to 1 litre of 100% acid.
• Therefore, the total amount of acid in the mixture is 6 litres.
• The strength of the mixture can be calculated by using the formula:
Mixture Strength = (M1 x Volume of 20% acid + M2 x Volume of 100% acid)/Total Volume
• Substituting the values, we get:
Mixture Strength = (20% x 5 litres + 100% x 1 litre)/10 litres
• Simplifying, we get:
Mixture Strength = (100 + 10)/10
• Therefore, the strength of the acid in the mixture is 60%.
Hence, the correct answer is Option C: 60%.

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