Correct reactivity order of alkyl halide towards dehydrohalogenation-

Which of the following gases is formed during the oxidation of trichloromethane?

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 one is liquid at room temperature?

$1,2-\text{dichloroethane} + NaSCH_2CH_2SNa \to C_4H_8S_2 + (P)$
Unknown product $(P)$ of the above reaction is

$KI$ in acetone undergoes $S_N2$ reaction with each $P, Q, R$ and $S$. The rates of the reaction vary as:
$P: CH_3-Cl$
$Q: (CH_3)_2CH-Cl$
$R: CH_2=CH-CH_2-Cl$
$S: C_6H_5-CO-CH_2-Cl$