The intermediate carbocation formed in the reactions of $\mathrm{HI}, \mathrm{HBr}$ and $\mathrm{HCl}$ with propene is the same and the bond energy of $\mathrm{HCl}, \mathrm{HBr}$ and $\mathrm{HI}$ is $430.5 \mathrm{kJ} {\mathrm{mol}}^{-1}, 363.7 \mathrm{kJ} {\mathrm{mol}}^{-1}$ and $296.8 \mathrm{kJ} {\mathrm{mol}}^{-1}$respectively. What will be the order of reactivity of these halogen acids?

What will be the product obtained as a result of the following reaction and why?

Arrange the following set of compounds In the order of their decreasing relative reactivity with an electrophile. Give reason.

Predict the major product (s) of the following reactions and explain their formation.

${\mathrm{H}}_3\mathrm{C}-\mathrm{CH}={\mathrm{CH}}_2\underset{\mathrm{HBr}}{\overset{(\mathrm{Ph}-\mathrm{CO}-\mathrm{O}{)}_2}{\to }}$

${\mathrm{H}}_3\mathrm{C}-\mathrm{CH}={\mathrm{CH}}_2\stackrel{\mathrm{HBr}}{\to }$

Nucleophiles and electrophiles are reaction intermediates having electron-rich and electron-deficient centres respectively. Hence, they tend to attack electron-deficient and electron-rich centres respectively. Classify the following species as electrophiles and nucleophiles. 

${\mathrm{H}}_3{\mathrm{CO}}^{-}$