$\mathrm{Xe}(g)+2 \mathrm{~F}_2(g) \xrightarrow[7 \text { bar }]{873 \mathrm{~K}} \mathrm{XeF}_4(\mathrm{~s})$

The ratio of $\mathrm{Xe}: \mathrm{F}_2$ required in the above reaction is

The density of nitric acid solution is $1.5 \mathrm{~g} \mathrm{~mL}^{-1}$. Its weight percentage is 68 . What is the approximate concentration (in $\mathrm{mol} \mathrm{L}^{-1}$ ) of nitric acid ?

$$ (\mathrm{N}=14 \mathrm{u} ; \mathrm{O}=16 \mathrm{u} ; \mathrm{H}=1 \mathrm{u}) $$

The concentration of 1 L of $\mathrm{CaCO}_3$ solution is 1000 ppm . What is its concentration in mol $\mathrm{L}^{-1}$ ?

$$ (\mathrm{Ca}=40 \mathrm{u}, \mathrm{O}=16 \mathrm{u}, \mathrm{C}=12 \mathrm{u}) $$