- An ice cube is a kind of substance
- An ice cube melts
- Melting means a substance changes from a solid into a liquid by increasing heat energy
- Hence, when an ice cube melts, it changes from a solid to a liquid

So, when an ice cube melts, it changes from a solid to a liquid
Question
When an ice cube melts, its state of matter changes from a

Context
- An ice cube is a kind of substance 
- An ice cube melts 
- Melting means a substance changes from a solid into a liquid by increasing heat energy