In presence of peroxide, hydrogen chloride and hydrogen iodide do not give anti-Markovnikov's addition to alkenes because

$2,3$-Dimethyl-$2$-butene can be prepared by heated which of the following compounds with a strong acid?

Acid-catalysed hydration of alkenes except ethene leads to the formation of

$2$-Phenylpropene on acidic hydration gives

On ozonolysis, one mole of a hydrocarbon produces two molecules of ethanal and one molecule of ethanedial. The hydrocarbon could be

An alkene on reductive ozonolysis gives two molecules of ${\mathrm{CH}}_2(\mathrm{CHO}{)}_2$. The alkene is