What is the number of electrons lost by Cr in a complex $\left[\mathrm{Cr}(\mathrm{CO})_6\right]$ ?

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.

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