The Diels-Alder reaction will not take place with which of the following reactants?

If the products of ozonolysis are acetone and formaldehyde,what is the starting substance?

Alkene $R-CH=CH_2$ reacts readily with $B_2H_6$ and the product on oxidation with alkaline hydrogen peroxide produces:

In the given reaction,$X$ will be:
Cyclohexene $\xrightarrow{NBS}$ $\xrightarrow[ether]{Mg}$ $\xrightarrow[2.H^{+}]{1.CO_2} X$

$A$ compound $X$ absorbs $2$ moles of hydrogen and $X$ upon oxidation with $KMnO_4 \mid H^{+}$ gives the products shown below:
$CH_3-CO-CH_3$,$CH_3-COOH$ and $CH_3-CO-CH_2-CH_2-COOH$.
The total number of $\sigma$ bonds present in the compound $X$ is . . . . . .

When $but-1-ene$ is mixed with an excess of bromine,the expected reaction product is: