The correct choice is (c) Calcium alginate
The best I can explain: The enzyme is linked to the carrier matrix by covalent binding between them. This is referred to immobilization by covalent binding. The function groups of the enzyme such as amino-acid group, sulphydryl, imidazole or free carboxyl groups are covalently linked to a carrier matrix. The most commonly used matrix are agarose, cellulose, polyacrylamide, glutaraldehyde, trialkoxysilanes etc. Calcium alginate is used for entrapment method of immobilization.