Step 1 - Understanding the law of mass conservation
In physics, chemistry and biology the law of mass conservation states that no atom is created or destroyed, they are only rearranged in any given physical/chemical/biological process.
Therefore, if all atoms are preserved, the total mass of reactants and products is the same.
Step 2 - Answering the exercise
The melting of an ice cube is a physical process and, as such, is also subjected to the law of mass conservation. Therefore, if 10g of ice melt, 10g of water are produced.
Answer: 10.0g