a number
Explanation:
Quantitative observation is taking any kind of measurement using a tool like measuring the volume of water or weighing the mass of a metal.
Qualitative observation is just a physical observation with no measurements involved.
1. Change of state is a qualitative observation. There is no measurement involved.
2. Change in size is a qualitative observation. There is no measurement involved.
3. A number is involved in a qualitative observation. Example: Measurement of length as 10 m.
4. Color is a qualitative observation. There is no measurement involved.