While combusting in air, $4 \ g$ of $H_2$ gas was completely converted into water. If $36 \ \mu mole$ of $CO_2$ from air is dissolved into that water, what is the concentration of $CO_2$?

The reaction of $1 \ mol$ of magnesium nitride with excess water gives:

$7.8 \ g$ of a compound having molecular formula $C_6H_6$,on reacting with $CH_3COCl / AlCl_3$ gives $8.4 \ g$ of a product which has molecular formula $C_8H_8O$. Calculate the percentage yield of the product $C_8H_8O$. (Given atomic weights of $H$,$C$ and $O$ respectively are $1$,$12$ and $16$) (in $\%$)

What volume in $mL$ of $96\% \, w/w \, H_2SO_4$ is required to prepare $2 \, L$ of $3 \, M \, H_2SO_4$ solution? (Density of $H_2SO_4$ solution $= 1.83 \, g/mL$)

Equal weights of methane and oxygen are mixed in an empty container at $25\,^{\circ}C$. The fraction of the total pressure exerted by oxygen is

The mass of iron converted into $Fe_3O_4$ by the action of $18\text{ g}$ of steam is : (Given: Molar mass of $H$, $O$ and Fe are $1$, $16$ and $56\text{ g mol}^{-1}$ respectively). Assume iron is present in excess: (in $\text{ g}$)