(d) All of the given options
The observations that help us for determining a chemical reaction are:
(a) Change in colour
(When sugar is heated it turns brown)
(b) Change in state
(Electrolysis of water in a liquid state gives off oxygen and hydrogen gases)
(c) Evolution of gas
(Ferric sulphate on heating gives ferric oxide and sulphur dioxide and sulphur trioxide gases are evolved).
