Select the correct statement(s) about chemical reaction in a closed container.

Total moles may change but mass remain constant. Let take a example of a chemical reaction.

${\mathrm{N}}_2+3{\mathrm{H}}_2\to 2{\mathrm{NH}}_3$

Here,
No. of moles in reaction = 1+3=4 moles
No. of moles in product = 2 moles
Thus, total moles not constant.
Total mass on reactant side $=m_{N2}+m_{H2}$

$\begin{array}{r}=28+3\times 2\\ =34\mathrm{g}\end{array}$

Total mass on product side =2×(14+3)
=34 g
Thus, total mass remain constant.