Explanation:

- Initially, the container has 20 liters of milk.

- After taking out 10 liters of milk and replacing it with water, you have 10 liters of milk left.

- The mixture is now half milk and half water.

- When you take out 10 liters of this mixture, 5 liters are milk and 5 liters are water.

- Replace this with 10 liters of water again.

- Now, you have only 5 liters of milk left in the container.

?? Correct Answer: Option 2 - 5 litres