Question

list any four changes around us which by observation can help us to determine whether a chemical reaction has occurred

Answer 1

1. A smell is obtained.
2. The container heats up.
3. Brisk effervescence is produced.
4. A gas is obtained which can be tested.

Answer 2

to determine mine chemicals change we see follow changes :-
01. change in state.
02. change in temperature.
03. change in color.
04. change in odour ( smell).