How many moles of electrons will weigh $1 \ kg$?

The total number of electrons in $18 \ mL$ of water (density $= 1 \ g \ mL^{-1}$) is

The number of moles of water present in a spherical water droplet of radius $1.0 \ cm$ is,(Given: Density of water in the droplet $= 1.0 \ g \ cm^{-3}$)

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 $24 \times 10^{23}$ molecules are removed from $50 \ g$ of hydrogen gas $(H_2)$,how many moles of hydrogen remain?

Numbers of gram atoms of oxygen present in $0.8 \ mol$ of $C_4H_6O_6$ would be