A mixed ether $(\mathrm{P})$, when heated with excess of hot concentrated hydrogen iodide produces two different alkyl iodides which when treated with aq. NaOH give compounds $(\mathrm{Q})$ and $(\mathrm{R})$. Both $(\mathrm{Q})$ and $(\mathrm{R})$ give yellow precipitate with NaOI . Identify the mixed ether $(\mathrm{P})$ :

Given below are two statements :

Statement I : The second ionisation enthalpy of Na is larger than the corresponding ionisation enthalpy of Mg .

Statement II : The ionic radius of $\mathrm{O}^{2-}$ is larger than that of $\mathrm{F}^{-}$.

In the light of the above statements, choose the correct answer from the options given below :

Both human DNA and RNA are chiral molecules. The chirality in DNA and RNA arises due to the presence of

A student has been given a compound " $x$ " of molecular formula- $\mathrm{C}_6 \mathrm{H}_7 \mathrm{~N}$. ' $x$ ' is sparingly soluble in water. However, on addition of dilute mineral acid, ' $x$ ' becomes soluble in water. ' $x$ ' when treated with $\mathrm{CHCl}_3$ and $\mathrm{KOH}(\mathrm{alc})$, ' $y$ ' is produced. ' $y$ ' has a specific unpleasant smell. On treatment with benzenesulphonyl chloride, ' $x$ ' gives a compound ' $z$ ' which is soluble in alkali. The number of different " H " atoms present in ' z ' is:-