Explanation:

- A tall order means something that is very hard to achieve or do.

- Option 1: A task difficult to perform – This fits well. A "tall order" is often said about something challenging to accomplish.

- Option 2: A bid problem – This is not correct. There is no phrase "bid problem", and "tall order" is not used this way.

- Option 3: A royal summon – This is unrelated. "Tall order" has nothing to do with royalty or summons.

- Option 4: A big demand – This is partly close, as it can refer to a difficult request, but it mainly stresses on difficulty, not just being "big".