Identify the reagent ' R ' used in the following reaction.

Ketone $\xrightarrow{\mathbf{R}}$ Semicarbazone

Identify alkadiene molecule from following.

Identify the product obtained in the following reaction.

$$\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br}+\mathrm{CH}_3 \mathrm{COOAg} \xrightarrow{\Delta} \mathrm{x}+\mathrm{AgBr}$$

Identify the reagent R used in following conversion?

tert-butyl bromide $\xrightarrow{\mathrm{R}}$ Isobutylene