The mass of water produced when $4 \ g$ of hydrogen reacts with $4 \ g$ of oxygen is .......... $g$.

$250 \ mL$ of $0.5 \ M \ NaOH$ was added to $500 \ mL$ of $1 \ M \ HCl$. The number of unreacted $HCl$ molecules in the solution after complete reaction is $...... \times 10^{21}$. (Nearest integer) $(N_{A} = 6.022 \times 10^{23})$

$A$ mixture containing $64.0 \ g$ of $H_2$ and $64.0 \ g$ of $O_2$ is reacted so that water is formed as follows:
$2H_2 + O_2 \rightarrow 2H_2O$
Which of the following statements is/are correct?

At $100\,^oC$,a $1.5\,L$ vessel contains $0.4\,g$ of $O_2$ and $0.06\,g$ of $H_2$. $(a)$ What is the total pressure in the vessel? $(b)$ If the mixture reacts to form water at $100\,^oC$,which gas will remain in the vessel? What will be their partial pressures (in $,atm$)? $(R = 0.0821\, L\,atm\,mol^{-1}\,K^{-1})$.

$KMnO_4$ reacts with $KI$ in basic medium to form $I_2$ and $MnO_2$. When $250 \ mL$ of $0.1 \ M \ KI$ solution is mixed with $250 \ mL$ of $0.02 \ M \ KMnO_4$ in basic medium,what is the number of moles of $I_2$ formed?

What is the maximum amount of $Cl_2$ gas produced when $1 \, g$ of $HCl$ and $1 \, g$ of $MnO_2$ are heated together (in $, g$)?