The molarity of pure water is ...... .

$A$ given initial mass of $KClO_3$ on $50\%$ decomposition produces $67.2 \ L$ of oxygen gas at $0 \ ^\circ C$ and $1 \ atm$. The other product of decomposition is $KCl$. The initial mass of $KClO_3$ (in $g$) taken is:

What is the value of percent atom economy if the molar mass of reactants is $36 \ u$ and the mass of the desired product is $27 \ u$ (in $\%$)?

$A$ metal chloride contains $55.0 \%$ of chlorine by weight. $100 \ mL$ of vapours of the metal chloride at $STP$ weigh $0.57 \ g$. The molecular formula of the metal chloride is $...$. (Given: Atomic mass of chlorine is $35.5 \ u$)

Sodium oxide reacts with water to produce sodium hydroxide. $20.0 \ g$ of sodium oxide is dissolved in $500 \ mL$ of water. Neglecting the change in volume,the concentration of the resulting $NaOH$ solution is $........ \times 10^{-1} \ M.$ (Nearest integer)
[Atomic mass $: Na=23.0, O=16.0, H=1.0]$

Volume of air needed for complete combustion of $10 \ L$ of $C_2H_4$ is :
$($Assume air contains $20\%$ of $O_2$ by volume$)$ (in $L$)