Rank the following groups in order of decreasing leaving group ability:
$(i)$ $-OSO_2C_6H_4CH_3$ (tosylate)
(ii) $-OCOCH_3$ (acetate)
(iii) $-OCH_3$ (methoxide)
(iv) $-OSO_2CF_3$ (triflate)

In the following reaction sequence,the correct structure$(s)$ of $X$ is (are)
$X$ $\xrightarrow[2) NaI, Me_2CO]{1) PBr_3, Et_2O}$ $\xrightarrow{3) NaN_3, HCONMe_2} \text{enantiomerically pure product}$

Which is the correct reaction coordinate diagram for the following solvolysis reaction?

Chloroform for anesthetic purposes is tested for its purity with the reagent

Under the specified conditions,substrate $X$ undergoes substitution and elimination reactions to give products $A - D$. $A$ and $B$ are stereoisomers,but not enantiomers. $C$ and $D$ are enantiomers. $A$ is not an isomer of $C$. Which of the following could be the starting material $X$ ?
$X \xrightarrow[\Delta]{H_2O} A + B + C + D$

The set of compounds in which the reactivity of the halogen atom increases in the order is ..........