<p>0.5g of fuming&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>H</mi><mn>2</mn></msub><mi>S</mi><msub><mi>O</mi><mn>4</mn></msub></math>&nbsp;(oleum) is diluted with water. This solution is completely neutralised by 26.7 mL of 0.4 N NaOH. The percentage of free&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>S</mi><msub><mi>O</mi><mn>3</mn></msub></math>&nbsp;in teh sample is:</p>