What quantity of $H_2O$ in grams is present in $0.25 \text{ mol}$ of it (in $\text{ g}$)?

How many moles of magnesium phosphate,$Mg_{3}(PO_{4})_{2}$ will contain $0.25 \ mol$ of oxygen atoms?

How many moles of any gas are present in $1 \ m^3$ at $NTP$?

$7.0 \, g$ of $N_2$,$8.0 \, g$ of $O_2$,and $34.0 \, g$ of $NH_3$ are present in a $1 \, L$ vessel. The active masses in $mol \, L^{-1}$ are respectively:

Among the following,choose the ones with an equal number of atoms.
$A$. $212 \ g$ of $Na_2CO_3(s)$ [molar mass $= 106 \ g/mol$]
$B$. $248 \ g$ of $Na_2O(s)$ [molar mass $= 62 \ g/mol$]
$C$. $240 \ g$ of $NaOH(s)$ [molar mass $= 40 \ g/mol$]
$D$. $12 \ g$ of $H_2(g)$ [molar mass $= 2 \ g/mol$]
$E$. $220 \ g$ of $CO_2(g)$ [molar mass $= 44 \ g/mol$]
Choose the correct answer from the options given below.

If $3.01 \times 10^{20}$ molecules are removed from $98 \ mg$ of $H_2SO_4$,how many moles of $H_2SO_4$ are removed?