An element $X$ reacts with oxygen to form a compound $X_2O_3$. If the atomic mass of $X$ is $91.5$,the equivalent mass of $X$ is:

The equivalent weight of which of the following is maximum? (Given: atomic weights $Na=23, Mn=55, Cr=52, K=39, O=16, C=12$)

Among $10^{-9} \ g$ (each) of the following elements,which one will have the highest number of atoms?
Element: $Pb, Po, Pr$ and $Pt$

Calculate the molecular mass of a glucose $C_{6}H_{12}O_{6}$ molecule.

Oxygen contains $90\%$ of $^{16}O$ and $10\%$ of $^{18}O$. Its atomic mass is

An element has three isotopes and their isotopic weights are $11, 12, 13$ units,and their percentage of occurrence in nature is $80 \%, 15 \%, 5 \%$ respectively. Then the average atomic weight of the element will be $:-$