Arrange the following hydrogen halides in order of their increasing reactivity with propene.

1. HCl>HBr>HI

2. HBr>HI>HCl

3. HI>HBr>HCl

4. HCl>HI>HBr

 
HINT: Reactivity of an acid inversely proportional to the bond energy
 
EXPLANATION
 
Bond energy of HI is 296.8 kJ/mol, HBr is 362.7 kJ/mol and HCl is 430.5 kJ/mol. As bond energy decreases the reactivity of
 
hydrogen halide compound increases. In the case of hydrogen halide, down the group reactivity increases with propene
 
Hence, HI>HBr>HCl is the order of reactivity with propene.