Assertion (A) $\mathrm{HNO}_3$ makes iron passive.

Reason (R) $\mathrm{HNO}_3$ forms a protective layer of ferric nitrate on the surface of iron.

Assertion (A) HI cannot be prepared by the reaction of KI with concentrated $\mathrm{H}_2 \mathrm{SO}_4$.

Reason $(\mathrm{R}) \mathrm{HI}$ has lowest $\mathrm{H}-\mathrm{X}$ bond strength among halogen acids.

Assertion (A) Both rhombic and monoclinic sulphur exist as $S_8$ but oxygen exists as $\mathrm{O}_2$.

Reason (R) 0xygen forms $p \pi$ - $p \pi$ multiple bond due to small size and small bond length but $p \pi-p \pi$ bonding is not possible in sulphur.

Assertion (A) NaCl reacts with concentrated $\mathrm{H}_2 \mathrm{SO}_4$ to give colourless fumes with pungent smell. But on adding $\mathrm{MnO}_2$ the fumes become greenish yellow.

Reason $(\mathrm{R}) \mathrm{MnO}_2$ oxidises HCl to chlorine gas which is greenish yellow.

Assertion (A) $\mathrm{SF}_6$ cannot be hydrolysed but $\mathrm{SF}_4$ can be.

Reason (R) Six F-atoms in $\mathrm{SF}_6$ prevent the attack of $\mathrm{H}_2 \mathrm{O}$ on sulphur atom of $\mathrm{SF}_6$.