Answer: describing how copper changes color in chlorine.
Explanation:
Quantitative observation is one which involves measurement of data in numbers.
Qualitative observation is one which can be observed with our senses such as sight, smell, touch, taste, and hearing. Qualitative observations do not involve any measurement.
Measuring the speed is a quantitative observation as it deals with numbers.
Describing how copper changes color in chlorine does not involve any numerical measurement hence a qualitative observation.
Recording how long it takes to burn magnesium is measuring time which is recorded in numbers and is a quantitative observation.
Showing the results of an experiment with a graph is data representation in numbers and is a quantitative observation.
