Which of the following substances generally has the highest melting point?

The number of secondary amines with the molecular formula $C_4H_{11}N$ is

The strongest base among the following is

Which of the following compounds is an example of a secondary amine?

Which compound is virtually non-basic?

Starting from propanoic acid,the following reactions were carried out: $CH_3-CH_2-COOH$ $\xrightarrow{SOCl_2} X$ $\xrightarrow{NH_3} Y$ $\xrightarrow{Br_2 + KOH} Z$. What is the compound $Z$?