Answer:
A change is said be chemical change when a change in chemical property of a substance occurs and the new substance is chemically different from old one. A change is said to be physical change when only physical properties change but chemically the substances remain same.
a) adding sugar to lemonade- It is a physical change because sugar is being dissolves in the lemonade. There is no change in the chemical property.
b) plants using CO₂ and H₂O to form O₂ and sugar is a chemical change because new products which are chemically different are formed.
c) boiling water - is a physical change because only the physical state from liquid to gas changes. Chemically water retains its properties.
d) frying an egg - the properties of egg changes after frying. Hence, it is a chemical change. A fried egg does not retain properties of an uncooked one.
e) rust forming on metal- is a chemical change. Corrosion ( rusting) is a chemical change as rust is chemically different from the metal.
f) fruit rotting - is a chemical change. When microbes act on the fruit, the fruit starts to rot.
g) removing salt from water by evaporation- it is a physical change. The salt and water retain their physical properties as mixture and when separated by evaporation process.