Which among the following statements is $NOT$ correct about $SN^2$ reaction mechanism?

The rate-limiting step of an $S_N1$ reaction follows the sequence shown below. Based on the assumption that $R$ contains $3$ different groups,which statement is true?
$\mathop R\limits^{\delta \oplus } \,\mathop {Br}\limits^{\delta \Theta } \, \rightleftharpoons \,\mathop {\boxed{{R^ \oplus }Br^\Theta }}\limits_{(a)} \,\,\, \rightleftharpoons \,\mathop {\boxed{{R^ \oplus }}\,\boxed{Br^\Theta }\,}\limits_{(b)} \,\, \rightleftharpoons $ ${\boxed{{R^ \oplus }}}$ $ + $ $\mathop {\,\boxed{Br^\Theta }\,}\limits_{(c)} \,$

Which is correct for the above reaction $:-$

Consider the given reaction: $CH_3-CH=CH-CH_2-OH \xrightarrow[S_N1]{HBr} [P]$. In the given reaction,the product $[P]$ is:

Identify the major product formed when propene is treated with hydrogen chloride followed by Swarts reaction.

Consider the following reaction. Which of the following products is not expected to be formed?
$CH_3CH_2CH(Br)CH_3 + HC \equiv C^- Na^+ \rightarrow ?$