Answer with Explanation:
There are two types of Observation:
1.→ Qualitative Observation : In which things are Selected on the basis of Quality ,like Color,Shape , Size ,Behavior,Nature of a person, etc...
2.→Quantitative Observation: Representation is done with the help of numbers ,Alphabets or Special Characters or by Combining all of them.
Option A: A Change of State: ------It denotes Quality.
Option B: A change in Size : ----It can be both Quality as well as Quantity.For Example Animal loosing and gaining weight can be represented in terms of both numbers as well Quality.For example :50-30,Fat-Thin.
Option C: A number-----It denotes Quantity.
Option D: A Color----It denotes Quality.
⇒A Number is : is must a quantitative observation.