Answer:
The correct answer will be option-B.
Explanation:
A scientific investigation involves many steps to answer and explain the natural phenomenon. The observational scientific investigation is a way which includes making an observation which is also the first step of the scientific method.
In the given question, observing the color of the solution while heating will be considered as an example of observational investigation as it states that something has been observed with the senses of the human. All other are cases of experimental investigation.
Thus, Option-B is the correct answer.
