The molecule ' $X$ ' has see-saw shape with central atom in $s p^3 d$ hybridisation. What is ' $X$ '?

Two vessels are filled with ideal gases $A$ and $B$ and are connected through a pipe of zero volume as shown in figure. The stop cock is opened and the gases are allowed to mix homogeneously and the temperature is

kept constant. The partial pressures of $A$ and $B$ respectively ( in atm ) are

If the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{MnO}_4^{-}$is $x$, the number of moles of $\mathrm{Fe}^{2+}$ ions oxidised by one mole of acidified $\mathrm{Cr}_2 \mathrm{O}_7^{2-}$ is

One mole of an ideal gas at 300 K and 20 atm expands to 2 atm under isothermal and reversible conditions. The work done by the gas is $-x \mathrm{~kJ} \mathrm{~mol}^{-1}$. The value of $x$ is $\left(R=8.3 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}\right)$