A mixture of $CaCO_3$ and $MgCO_3$ weighing 1.84 g on heating leaves a residue weighing 0.96 g. If the percentage by mass of $CaCO_3$ in the original mixture is x%, what is the value of x/2?

2.24 L of a gas at STP weighs 3.2 g. The molecular weight of the gas is:

Which of the following contains the greatest number of atoms?

$26\,{\rm{mL}}$ of ${\rm{C}}{{\rm{O}}_2}$ are passed over hot coke. The maximum volume of CO formed is :

13.5 g aluminium changes to ${\rm{A}}{{\rm{l}}^{3 + }}ion$ in solution by losing :

Equal masses of oxygen and ozone are present in a container at 298 K. The ratio of their partial pressures ($P_{O_2} : P_{O_3}$) is:

In which case is the number of molecules of water maximum ?

Upon heating, 15.0 g of impure zinc carbonate decomposes completely to produce zinc oxide and carbon dioxide. If 5.6 g of zinc oxide is formed, calculate the percentage purity of the zinc carbonate sample. (Atomic weight: $Zn = 65.4$)

A mixture of ${\rm{2}}{\rm{.3}}\,\,{\rm{g}}$ formic acid and ${\rm{4}}{\rm{.5}}\,\,{\rm{g}}$ oxalic acid is treated with conc. ${{\rm{H}}_{{\rm{2}}\,}}{\rm{S}}{{\rm{o}}_{\rm{4}}}$ . The evolved gaseous mixture is passed through ${\rm{KOH}}$ pellets weight (in g) of the remaining product at STP will be

Which sample contains the largest number of helium atoms?

If you have 18g of water and 18g of oxygen, which contains a greater number of molecules?