How many moles of $Mg_3(PO_4)_2$ contain $0.25$ moles of oxygen atoms?

The mass of a sample of aluminum is $54 \ g$. The mass of the same number of magnesium atoms will be ......... $g$.

Calculate the number of atoms in the following: $(i)$ $52 \ mol$ of $Ar$ $(ii)$ $52 \ u$ of $He$ $(iii)$ $52 \ g$ of $He$

Which of the following substances consists of a total of $1 \ mol$ of atoms? (Molar mass of $NH_3 = 17 \ g/mol, H_2O = 18 \ g/mol, N_2 = 28 \ g/mol, CO_2 = 44 \ g/mol$)

The number of $Cl^{-}$ ions in $333 \ g$ of anhydrous $CaCl_2$ will be ................ $N_A$.

The number of molecules in $16 \ g$ of methane is