10 litre solution of urea contains 240 g urea. The active mass of urea will be :

We know that molar concentration of a substance is called its active mass . 10 L of urea solution contains urea =240g 1 L of urea solution contains urea=240g10=24gg. mol. wt. of urea,  NH2CONH2                       =14+(2×1)+12+16+14+(2×1) =60gNo. of mol of urea      = wt. of urea  g. mol. wt. of urea =24g60g=0.4