The capacities of three containers X, Y and Z are 1, 2 and 4 liters respectively. Initially, X is empty, while Y and Z are full of water and milk respectively. X is filled from Y, Y is replenished from Z and X is emptied into Z. If this process is repeated once more, then what will be the ratio of milk in Y to water in Z?

Let's break down the process step by step:

1. Initially, X is empty, Y is full of water (2 liters), and Z is full of milk (4 liters).

2. X is filled from Y. Now, X has 1 liter of water, Y has 1 liter of water left, and Z still has 4 liters of milk.

3. Y is replenished from Z. Now, Y is full again with 1 liter of water and 1 liter of milk, and Z has 3 liters of milk left.

4. X is emptied into Z. Now, X is empty, Y still has 1 liter of water and 1 liter of milk, and Z has 3 liters of milk and 1 liter of water.

5. The process is repeated. X is filled from Y (which contains half water and half milk). Now, X has 0.5 liter of water and 0.5 liter of milk, Y has 0.5 liter of water and 0.5 liter of milk left, and Z still has 3 liters of milk and 1 liter of water.

6. Y is replenished from Z (which contains mostly milk). Now, Y is full again with 0.5 liter of water, 1 liter of milk, and 0.5 liter of milk from Z. Z now has 2.5 liters of milk and 1 liter of water.

7. X is emptied into Z. Now, X is empty, Y has 0.5 liter of water and 1.5 liters of milk, and Z has 3 liters of milk, 1 liter of water, and 0.5 liter of water and 0.5 liter of milk from X.

So, the ratio of milk in Y to water in Z is 1.5:1.5, or 1:1.