Right option is (b) covalent binding
The explanation: In the immobilization method by covalent binding, the enzyme is linked to the carrier matrix by covalent bond between them. This method allows strong binding with little or no leakage of enzyme. This method allows less enzyme loading capacity. Adsorption method of immobilization involves binding of enzyme to suitable adsorbent which renders it immobile. The entrapment method of immobilization involves the entrapment of enzyme within suitable gel or fibers. Immobilization by membrane confinement involves confining the enzyme in aqueous solution within a semipermeable membrane.