Explanation:

- Estoppel is a legal principle that prevents someone from arguing something contrary to a previous claim or behavior that has been relied upon by others.

- Option 1: Question of facts

- Deals with factual scenarios where one cannot deny facts once they've been established.

- Option 2: Question of right

- Involves legal rights or entitlements, not typically related to estoppel.

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

- Suggests estoppel covers both facts and rights, which isn’t entirely accurate; estoppel is primarily fact-based.

- Option 4: Neither (a) nor (b)

- Incorrect, as estoppel clearly relates to facts.

Correct Answer: Option 1 - Question of facts