Explanation:

- The cube has a side length of 10 cm and weighs 200 grams.

- The volume of the cube is $10\times 10\times 10=1000{\text{cm}}^3$.

- Since the cube is hollow, its weight is 200 grams.

- In water, the weight of water displaced equals the weight of the cube.

- Density of water is $1{\text{g/cm}}^3$, so it weighs 1 gram per cm of height for a 100 cm${}^2$ base.

- To displace 200 grams, the sunken height $h$ should satisfy: 100 cm${}^2$ × $h$ cm = 200 grams, which means $h=2\text{cm}$.

- Answer: 3. 2 cm