Question

in surface chenistry why there is preferential adsorption and why its happen.

Answer 1

when u consider he material there are two types of molecules u can find one present at the surface and other present at the bulk.
if u carefully observe the bulk molecules are saturated,mean they have connected to its surrounding molecules completely.
where as the molecules at the surface where surrounded half of them and other half is present on surface , so they are unsaturated mean still they can form bond on the surface
so it adsorbs some adsorbing material on its surface