Which is an example of making a qualitative observation?
a. measuring the speed of the chemical reaction
b. describing how copper changes color in chlorine
c. recording how long it takes to burn magnesium
d. showing the results of an experiment with a graph

Option (b) is the correct answer.

Explanation:

A quantitative data is defined as the data which can only be described in numbers or figures.  

For example, mass of an object is 50 kg.

This is a quantitative data as mass is represented in figures.

On the other hand, a data which describes the nature of a substance and that can only be described in words as there will be no figures or numerical data then it is known as a qualitative data.

For example, describing how copper changes color in chlorine is a qualitative data.

Thus, we can conclude that describing how copper changes color in chlorine  is an example of making a qualitative observation.

d

explanation:

v=uf/(u-f)

= 5.10/(5-10) convex lens has positive focal length

=50/-5

=-10 cm (formed at other side)

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000