Nitrosobenzene can be prepared by oxidizing aniline with which of the following reagents?

The products $A$ and $B$ formed in the following reaction scheme are respectively:

The reaction of $HNO_2$ with $A$ gives a quaternary ammonium salt. $A$ is

The major product obtained in the following reaction is:

Identify the major product of the following Hofmann elimination reaction: $[\text{cyclohexyl-}N^{+}(CH_3)(CH_2CH_3)(n\text{-Bu})]OH^{-} \xrightarrow{\Delta} \text{Major product}$

Yellow dye can be prepared by a coupling reaction of benzene diazonium chloride in acidic medium with $X$. Identify $X$ from the following.