When orthoboric acid $\left(\mathrm{H}_3 \mathrm{BO}_3\right)$ is subjected to strong heating, the residue left is

When graphite is heated at $300^{\circ} \mathrm{C}$ with potassium vapour, it forms $\mathrm{C}_8 \mathrm{~K}$ compound that shows one of the following property.

Which of the following molecules is present in photochemical smog?

The correct order of the relative stability of the following carbanions is

I. $\mathrm{HC} \equiv \mathrm{C}^{-}$

II. $\mathrm{CH}_2=\mathrm{CH}-\mathrm{CH}_2^{-}$

III. $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$

IV. $\left(\mathrm{C}_6 \mathrm{H}_5\right)_2 \mathrm{CH}^{-}$