5.00 mL of 0.10 M oxalic acid solution taken in a conical flask is titrated against NaOH from a burette using phenolphthalein indicator. The volume of NaOH required for the appearance of permanent faint pink color is tabulated below for five experiments. What is the concentration, in molarity, of the NaOH solution?

Exp. No.	Vol. of NaOH (mL)
1	12.5
2	10.5
3	9.0
4	9.0
5	9.0

The mole fraction of urea in an aqueous urea solution containing 900 g of water is 0.05. If the density of the solution is 1.2 g cm^$$-$$3, then molarity of urea solution is ................

(Given data : Molar masses of urea and water are 60 g mol^$$-$$1 and 18 g mol^$$-$$1, respectively)

The amount of water produced (in g) in the oxidation of 1 mole of rhombic sulphur by conc. HNO₃ to a compound with the highest oxidation state of sulphur is ..............

(Given data : Molar mass of water = 18 g mol^$$-$$1)

To measure the quantity of $$MnC{l_2}$$ dissolved in an aqueous solution, it was completely converted to $$KMn{O_4}$$ using the reaction,

$$MnC{l_2} + {K_2}{S_2}{O_8} + {H_2}O \to KMn{O_4} + {H_2}S{O_4} + HCl$$ (equation not balanced).

Few drops of concentrated $$HCl$$ were added to this solution and gently warmed. Further, oxalic acid ($$225$$ $$mg$$) was added in portions till the colour of the permanganate ion disappeared. The quantity of $$MnC{l_2}$$ (in mg) present in the initial solution is ____________.

(Atomic weights in $$g\,\,mo{l^{ - 1}}:Mn = 55,Cl = 35.5$$ )