Ionic species are stabilised by the dispersal of charge. Which of the following carboxylate ion is the most stable?

Electrophilic addition reactions proceed in two steps. The first step involves the addition of an electrophile. Name the type of intermediate formed in the first step of the following addition reaction. $$\mathrm{H}_3 \mathrm{C}-\mathrm{HC}=\mathrm{CH}_2+\mathrm{H}^{+} \longrightarrow \text { ? }$$

Covalent bond can undergo fission in two different ways. The correct representation involving a heterolytic fission of $\mathrm{CH}_3-\mathrm{Br}$ is

The addition of HCl to an alkene proceeds in two steps. The first step is the attack of $\mathrm{H}^{+}$ion to

portion which can be shown as

Which of the following compounds contain all the carbon atoms in the same hybridisation state?