What quantity of oxygen is required for complete burning of $15.6 \ g$ benzene (in $g$)?

What is the weight in $g$ of $90\%$ pure $H_2SO_4$ required to neutralize $5 \ g$ of caustic soda?

How many litres of oxygen (at $STP$) are required for complete combustion of $39 \ g$ of liquid benzene?
(Atomic weights: $C=12, O=16, H=1$)

Haemoglobin contains $0.33\%$ of iron by weight. The molecular weight of haemoglobin is approximately $67200$. The number of iron atoms (At. wt. of $Fe = 56$) present in one molecule of haemoglobin is

If $6.022 \times 10^{20}$ atoms are present in $100 \ mL$ of urea solution,then find out the molarity of the urea solution. (in $M$)

Find the molecular weight of a solid containing $20\%$ by mole of $S$ atoms,whose $400\ g$ provides just sufficient $S$ atoms to produce enough $H_2SO_4$ to neutralise $100\ g$ $NaOH$.