An LPG (Liquified Petroleum Gas) cylinder weighs 15.0 kg when empty. When full, it weighs 30.0 kg and shows a pressure of 3.0 atm . In the course of usage at $27^{\circ} \mathrm{C}$, the mass of the full cylinder is reduced to $24 \cdot 2 \mathrm{~kg}$. The volume of the used gas in cubic metre at the normal usage condition ( atm and $27^{\circ} \mathrm{C}$ ) is (assume LPG to be normal butane and it behaves ideally)

What is the four-electron reduced form of $\mathrm{O}_2$ ?

Kjeldahl's method cannot be used for the estimation of nitrogen in which compound?

Which of the following compounds is most reactive in $\mathrm{S}_{\mathrm{N}} 1$ reaction?