The mass of a mixture containing NaCl and NaBr is 4.0 g . If Na is $30 \%$ of the total mixture, the composition of NaCl in the mixture is $(\mathrm{Na}=23 \mathrm{u}, \mathrm{Cl}=35.5 \mathrm{u}, \mathrm{Br}=80 \mathrm{u})$

Two acids $A$ and $B$ are titrated separately, 25 mL of $0.5 \mathrm{M} \mathrm{Na}_2 \mathrm{CO}_3$ solution requires 10 mL of $A$ and 40 mL of $B$ for complete neutralisation. The volume (in L ) of $A$ and $B$ required to produce 1 L of 1 N acid solution respectively are

An ideal gas mixture of $\mathrm{C}_2 \mathrm{H}_6$ and $\mathrm{C}_2 \mathrm{H}_4$ occupies a volume of 28 L at 1 atm and 273 K . This mixture reacts completely with 128 g of $\mathrm{O}_2$ to produce $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}(l)$. What is the mole fraction of $\mathrm{C}_2 \mathrm{H}_4$ in the mixture ?

Complete combustion of ethane gives only gaseous products. In a closed vessel, 15 g of ethane and 112 g of $\mathrm{O}_2$ were allowed to completely react. What is the total number of moles of gaseous substances present in the vessel at the end of the reaction?