Fluorine and chlorine reacts with water but bromine and iodine are sparingly soluble in water .., what is the reason for such behaviour??
The halogens are insoluble in water, however the extent to which they react with water is different. Fluorine is a strong oxidising agent that oxidises water to dioxygen. The reaction is spontaneous and highly exothermic. A similar reaction occurs between chlorine and water. But this reaction is very slow. Therefore we have
X2 + 3H2O -------> 2H3O+ + 2X- + 1/2 O2
where X = F and Cl
Bromine and Iodine on the other hand, do not react with water. Both of them only undergo weak disproportionation in water. The basic reason for this is that while fluorine and chlorine are strong oxidising agents, bromine and iodine are weak oxidizing agents.
As fluorine and chlorine are relatively much smaller than bromine and iodine, hence they can accept electrons more readily than bromine and iodine. Therefore they are stronger oxidising agents than Br2 and I2.