In this question, we are given the prices of different fruits in terms of each other.

Option 1: If a mango costs 9, then 9 mangoes would cost 81. However, we are told that 9 mangoes are equivalent to 5 oranges, so this option does not fit the given information.

Option 2: If a mango costs 12, then 9 mangoes would cost 108. We are told that 9 mangoes are equivalent to 5 oranges, so this option satisfies the given information.

Option 3: If a mango costs 18, then 9 mangoes would cost 162. This does not fit the given information.

Option 4: If a mango costs 27, then 9 mangoes would cost 243. This option does not fit the given information.

Therefore, the correct answer is option 2. A mango will cost 12, based on the given information.