Explanation:

- Option 1: A contracting party is generally not obliged to disclose everything to the other party. The principle of "caveat emptor" (let the buyer beware) applies, meaning each party should do their due diligence.

- Option 2: The case, *Keates v The Earl of Cadogan* (1851), is indeed related to the notion that mere silence does not constitute fraud, emphasizing that non-disclosure of certain facts does not automatically imply deceit.

- Option 3: Both option (a) and option (b) are true, as they both reflect established principles in contract law.

- Option 4: Incorrect, because both statements (a) and (b) are true.

Correct Answer: Option 3 – Both (a) and (b)