Q. Which of the following are the observations of the chemical reaction?
  1. Change in state
  2. Evolution of a gas
  3. Change in colour
  4. Change in temperature
Select the correct answer from the codes given below:

Answer: All of the above
Notes: We can say that any of the following observations helps us to determine whether a chemical reaction has taken place or not :
  1. Change in state
  2. Change in colour
  3. Evolution of a gas
  4. Change in temperature.
As we observe the changes around us, we can see that there are many chemical reactions taking place around us.