When a jar containing a gaseous mixture of equal volumes of $CO_2$ and $H_2$ is placed in a solution of sodium hydroxide,the solution level will:

If $10^{21}$ molecules are removed from $100 \, mg$ of $CO_2$,how many moles of $CO_2$ remain?

What is the actual volume occupied by water molecules present in $20 \ cm^3$ of water (in $cm^3$)?

The correct order of the total number of atoms present in
$(A)$ $2$ moles of cyclohexane
$(B)$ $684 \text{ g}$ of sucrose
$(C)$ $90.8 \text{ L}$ of dihydrogen at $STP$
is:

When metallic copper comes in contact with moisture,a green powdery/pasty coating can be seen over it. This is chemically known as

The incorrect postulates of the Dalton's atomic theory are :
$A$. Atoms of different elements differ in mass.
$B$. Matter consists of divisible atoms.
$C$. Compounds are formed when atoms of different element combine in a fixed ratio.
$D$. All the atoms of given element have different properties including mass.
$E$. Chemical reactions involve reorganisation of atoms.
Choose the correct answer from the options given below :