Explanation:

- Section 81 of the IPC deals with acts committed to prevent harm.

- Option 1: Prevention of harm to person

- This implies acting to stop potential injury or damage to a person.

- Option 2: Prevention of harm to property

- This means actions taken to stop damage or risk to property.

- Option 3: Both (a) and (b)

- This suggests that the motive could encompass preventing harm to both a person and property.

- Option 4: Either (a) or (b)

- This indicates that the motive can be to prevent harm to either a person or property, but not necessarily both.

Correct Answer: Option 4: Either (a) or (b)

Motive under Section 81 can be to prevent harm to either a person or property.