$28 \ g$ $KOH$ is required to completely neutralize $CO_2$ produced on heating $60 \ g$ of impure $CaCO_3$. The percentage purity of $CaCO_3$ is approximately (molar masses of $KOH$ and $CaCO_3$ are $56$ and $100 \ g \ mol^{-1}$, respectively).

Diatoms,microscopic organisms,are an abundant food source in the oceans producing carbohydrates from carbon dioxide and water by photosynthesis.
$6CO_2 + 6H_2O + \text{solar energy} \to C_6H_{12}O_6 + 6O_2$
$A$ blue whale gains $75 kg$ of mass per day by feeding on krill. The whale must consume ten times this mass of krill each day. The krill must consume $10.0 kg$ of diatoms to produce $1.0 kg$ of krill. Assuming that the mass gain of a whale's life is due to the consumption of carbohydrates $(C_6H_{12}O_6)$,calculate the moles of $CO_2$ that must be used by the diatoms to produce the carbohydrates consumed by a blue whale in a day.

The molarity of $0.2 \ N$ $Na_2CO_3$ solution will be (in $M$)

For the complete combustion of $1 \, mol$ of a compound with the molecular formula $C_xH_yO_z$,the number of moles of $O_2$ required is:

Methylation of $10 \ g$ of benzene gave $9.2 \ g$ of toluene. Calculate the percentage yield of toluene $......$. (Nearest integer)

$1.5 \ mol$ of $O_2$ combine with $Mg$ to form oxide $MgO$. The mass of $Mg$ (atomic mass $24$) that has combined is ............. $g$.