4. This metal (X) displaces copper from copper sulphate solution but does not
displace zinc from zinc sulphate. From this we can tell that the order of reactivity
(most reactive first) is
a. zinc; copper; X
b. zinc; X ; copper
c. copper ; X ; zinc
d. X; zinc; copper;

Explanation:

B

quartz

explanation:

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.