How many moles of potassium chlorate need to be heated to produce $5.6 \, L$ of oxygen at $STP$?

$20 \ mL$ of methane is completely burnt using $50 \ mL$ of oxygen. The volume of the gas left after cooling to room temperature is (in $mL$)

$20 \, mL$ of a $1 \, N$ solution of $KMnO_4$ just reacts with $20 \, mL$ of a solution of oxalic acid. The weight of oxalic acid crystals in $1 \, L$ of the solution is $... \, g$

$A$ solution $(5 \, mL)$ of an acid $X$ is completely neutralized by $y \, mL$ of $1 \, M \, NaOH$. The same volume $(y \, mL)$ of $1 \, M \, NaOH$ is required to neutralize $10 \, mL$ of $0.6 \, M \, H_2SO_4$ completely. The normality $(N)$ of the acid $X$ is $......$

$A$ gas mixture contains $25 \%$ He and $75 \% CH_4$ by volume at a given temperature and pressure. The percentage by mass of methane in the mixture is approximately . . . . . . (in $\%$)

How much of $NaOH$ (in $g$) is required to neutralize $1500 \ cm^3$ of $0.1 \ N \ HCl$? (Given: $Na = 23, O = 16, H = 1$)