One mole of oxygen gas at $STP$ is equal to

What will be the mass of one atom of $^{12}C$ in grams?

$1 \ mL$ of water has $25$ drops. Let $N_0$ be the Avogadro number. What is the number of molecules present in $1$ drop of water? (Density of water $= 1 \ g / mL$)

The total number of protons in $10 \ g$ of $CaCO_3$ is = ......

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.

What is the volume occupied by $16 \ g$ methane gas at $STP$ (in $cm^3$)?