Number of $\pi$ bonds in $CH_2=CH-CH=CH-C\equiv CH$ is

What is the difference in terms of molar masses of the second and fourth members of a homologous series?

Addition of a mineral acid to an olefin bond leads to a major product. Identify it.

The dibromo compound $[P]$ (molecular formula : $C_{9}H_{10}Br_{2}$) when heated with excess sodamide followed by treatment with dilute $HCl$ gives $[Q]$. On warming $[Q]$ with mercuric sulphate and dilute sulphuric acid yields $[R]$ which gives positive Iodoform test but negative Tollen's test. The compound $[P]$ is:

The major product $A$ is:

The product $(Z)$ is: