why obritals combine or mixed to form hybrid orbitals?and than take part in reaction...............

hybridisation (or hybridization) is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties

well this is hypothetical concept!!!!!!!!!

The hybridisation theory was promoted by chemist Linus Pauling^[2] in order to explain the structure of molecules such as methane (CH₄). This concept was developed for such simple chemical systems, but the approach was later applied more widely, and today it is considered an effective heuristic for rationalizing the structures of organic compounds.