Explanation:

- Option 1: Is an offence

- Illegal acts are often criminal offences punishable by law.

- Examples include theft and assault.

- Option 2: Is prohibited by law

- Illegal actions are those forbidden by statutes or regulations, regardless of whether they are crimes.

- Examples include parking violations and jaywalking.

- Option 3: Furnishes ground for a civil action

- Not all illegal actions are criminal; some may result in civil lawsuits.

- Examples include breaches of contract and defamation.

- Option 4: All are correct

- An action can be illegal if it is a criminal offence, prohibited by law, or provides grounds for civil action.

Correct Answer: Option 4 - All are correct.