Half life of zero order reaction $\mathrm{A} \rightarrow$ product is 1 hour, when initial concentration of reactant is $2.0 \mathrm{~mol} \mathrm{~L}{ }^{-1}$. The time required to decrease concentration of A from 0.50 to $0.25 \mathrm{~mol} \mathrm{~L}^{-1}$ is :

The incorrect relationship in the following pairs in relation to ionisation enthalpies is :

A toxic compound " A " when reacted with NaCN in aqueous acidic medium yields an edible cooking component and food preservative " B ". " B " is converted to " C " by diborane and can be used as an additive to petrol to reduce emission. "C" upon reaction with oleum at $140^{\circ} \mathrm{C}$ yields an inhalable anesthetic " D ". Identify " A ", " B ", " C " & " D ", respectively :

In which pairs, the first ion is more stable than the second?