Which of the following is added to chloroform to slow down its aerial oxidation in the presence of light?

The ease of dehydrohalogenation of alkyl halide with alcoholic $KOH$ is:

Which of the following,when undergoing addition of $HBr$,will form $ONLY$ a pair of diastereomers?

Which of the following compounds is most reactive in $S_N 1$ reaction?

For the reactions given below:
$(I)$ Cyclohexyl chloride $\rightarrow$ Cyclohexyl cation + $Cl^-$,$\Delta H_1^{\circ}$
$(II)$ Cyclohex$-2-$enyl chloride $\rightarrow$ Cyclohex$-2-$enyl cation + $Cl^-$,$\Delta H_2^{\circ}$
$(III)$ Benzyl chloride $\rightarrow$ Benzyl cation + $Cl^-$,$\Delta H_3^{\circ}$
$(IV)$ Chlorobenzene $\rightarrow$ Phenyl cation + $Cl^-$,$\Delta H_4^{\circ}$
The correct decreasing order of enthalpies of reaction for producing the carbocation is:

When $1-$chlorobutane is treated with aqueous $KOH$,it gives $P$. However,when it is treated with alcoholic $KOH$,it gives $Q$. Identify the products $P$ and $Q$ respectively.