Question

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Answer 1

In a 90% H2SO4 by mass solution, 90% of the total mass of the solution is H2SO4 

So in 100 g of solution there will be 
90 g H2SO4 and 
10 g H2O = 0.01 kg H2O 

moles H2SO4 = mass / molar mass = 90 g / 98.076 g/mol = 0.9176557 mol 
total volume of 100 g of solution = mass / density = 100 g / 1.83 g/ml = 85.64 ml = 0.05464 L 

molarity = moles solute / lites solution 
= 0.9176557 mol / 0.05464 L 
= 16.8 M 

molality = moles solute / kg solvent 
= 0.9176557 mol / 0.01 kg 
= 91.8 m