When one or more properties of a material become different we say that a ___________ has taken place in it.
Whenever the colour, density, hardness, melting, and boiling point of a substance alters, we say that it has undergone a change.
When water is frozen, it forms ice that has different properties. Why then do we say that freezing is a physical change?
When a substance adds hydrogen to it or eliminate oxygen from it, we say that the substance has been ———(oxidised/reduced)