Choose the correct synonym of the following word: CONUNDRUM

The correct answer is Option (3) → Riddle

• Conundrum means a confusing and difficult problem or question; it is also used for a riddle whose answer involves a play on words.
  Example: How to cut costs without losing staff was a real conundrum for the manager.
• Riddle means a puzzling question that is hard to answer, or a mystery that is hard to understand. Both words name a puzzling problem, so riddle is the synonym of conundrum.
  Example: The children tried to solve the riddle in the magazine.

Why the Other Options are Incorrect?

Option 1: Idea — Incorrect. An idea is a thought or a plan in the mind; it has nothing puzzling about it.
Example: She had a good idea for the school project.

Option 2: Confession — Incorrect. A confession is an admission of a fault or crime; it is not a puzzle.
Example: The thief made a full confession to the police.

Option 4: Conference — Incorrect. A conference is a formal meeting for discussion; it only sounds a little like conundrum.
Example: Doctors from many countries attended the conference.