Which of the following gives the highest yield of $2$-pentene upon reaction with $C_2H_5ONa/C_2H_5OH$?

For the following reactions,which of the following statements is correct?
$A. \, CH_3CH_2CH_2Br + KOH \rightarrow CH_3CH=CH_2 + KBr + H_2O$
$B. \, (CH_3)_2CHBr + KOH \rightarrow (CH_3)_2CHOH + KBr$
$C. \, C_6H_{10} + Br_2 \rightarrow C_6H_{10}Br_2$

Arrange the following compounds in decreasing order of the rate of electrophilic addition reaction:
$(P)$ $p$-vinylbenzaldehyde
$(Q)$ $p$-vinylanisole
$(R)$ $p$-methylstyrene
$(S)$ $p$-dimethylaminostyrene

$S_N^1$ and $S_N^2$ reactions are

In the given reaction
$CH_3-CH(OTs)-CH_2-CH_2-CH(OTs)-CH_3$ $\xrightarrow[(ii) \ KOH]{(i) \ SH^{\ominus} (one \ equivalent)}$ $[X]$
$[X]$ will be :

Most reactive compound toward $S_N1$ is