In which of the following the $s$-block elements are arranged in the correct order of their melting points?
The correct statements about the compounds of boron are
I. In borax bead test, the colour of cobalt metaborate is blue.
II. Diborane is prepared by the oxidation of sodium borohydride with iodine.
III. In diborane oxidation state of hydrogen is +1 .
IV. Boric acid is a tribasic acid.
Dehydration of an organic acid $X$ with concentrated $\mathrm{H}_2 \mathrm{SO}_4$ at 373 K gives $\mathrm{H}_2 \mathrm{O}$ and gas $Y$. The hybridisation of the carbon in $Y$ and nature of $Y$ are respectively.
Identify the correct statements from the following
I. Photochemical smog has high concentration of oxidising agents.
II. $\mathrm{NO}_2$ is present in classical smog.
III. Higher concentration of $\mathrm{SO}_2$ in air can cause stiffness of flower buds.
IV. pH of rain water is approximately 7.5 .
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