An immobilized enzyme is an enzyme attached to an inert, insoluble material—such as calcium alginate. This can provide increased resistance to changes in conditions such as pH or temperature. so, op D.

Enzyme immobilization is the process of physically or chemically attaching an enzyme to a solid support, thereby restricting its movement and confining it to a specific location. This immobilized form of the enzyme can perform catalytic reactions while being protected and stabilized by the support matrix. It offers several advantages over free enzymes, including enhanced stability, reusability, and easy separation from the reaction mixture.

The correct answer is option 'D' - providing the enzyme with a protective covering. This is because enzyme immobilization involves attaching the enzyme to a solid support, which acts as a protective covering, shielding the enzyme from harsh reaction conditions and proteolytic degradation.

Here is a detailed explanation of enzyme immobilization:

1. Definition:
- Enzyme immobilization refers to the process of attaching an enzyme to a solid support or matrix.

2. Purpose and Benefits:
- Enhanced stability: Immobilization protects the enzyme from denaturation caused by changes in pH, temperature, or organic solvents.
- Reusability: Immobilized enzymes can be reused multiple times, reducing the need for enzyme replenishment.
- Easy separation: Immobilized enzymes can be easily separated from the reaction mixture by filtration or centrifugation, simplifying downstream processing.
- Increased enzyme concentration: Immobilization allows for higher enzyme concentrations in the reaction mixture, leading to improved reaction rates.
- Improved enzyme selectivity: Immobilized enzymes can selectively catalyze specific reactions due to their confined environment.

3. Methods of Immobilization:
a) Physical adsorption: The enzyme is attached to the support through weak interactions like hydrophobic interactions, electrostatic interactions, or hydrogen bonding.
b) Covalent binding: The enzyme is covalently attached to the support through chemical reactions, such as cross-linking or covalent bonding.
c) Entrapment: The enzyme is physically trapped within a gel or polymer matrix, which acts as a support.

4. Support Materials:
- Support materials can include natural polymers (e.g., agarose, cellulose), synthetic polymers (e.g., polyacrylamide, polystyrene), or inorganic materials (e.g., silica, aluminum oxide).

In conclusion, enzyme immobilization involves attaching an enzyme to a solid support, providing it with a protective covering that enhances its stability, allows for reusability, and simplifies separation. This immobilization process has various applications in industries such as food processing, pharmaceuticals, and biotechnology, where enzymes play a crucial role in catalyzing specific reactions.