Change in volume when $10 \, mL$ of phosphine $(PH_3)$ is decomposed according to the reaction: $2PH_{3(g)} \rightarrow 2P_{(s)} + 3H_{2(g)}$.

The right option for the mass of $CO_2$ produced by heating $20 \ g$ of $20 \%$ pure limestone is $........ \ g$ (Atomic mass of $Ca = 40$) $[CaCO_3 \stackrel{1200 \ K}{\longrightarrow} CaO + CO_2]$

The mass of nitrogen that combines with $40 \ g$ of oxygen in $N_2O_5$ is ............ $g$.

In the bromination of propyne,$1,1,2,2-$tetrabromopropane is obtained in $27\%$ yield. The amount of $1,1,2,2-$tetrabromopropane obtained from $1 \; g$ of bromine $(Br_2)$ in this reaction is $\dots \; \times 10^{-1} \; g$. (Nearest integer)
(Molar mass: Bromine $(Br)$ $= 80 \; g/mol$)

What volume of decimolar solution should be mixed in a solution of the same solute $(0.5 \, M, \, 200 \, mL)$ to make it $0.25 \, M$?

Equal masses of $H_2, O_2$ and methane have been taken in a container of volume $V$ at temperature $27 \ ^oC$ in identical conditions. The ratio of the volumes of gases $H_2 : O_2 :$ methane would be