ANSWER
The number of students who like chemistry labs but not physical science is 12.
Step-by-step explanation
The total number of students in the science class are 30.
The number of students who do chemistry lab is 19.
The number of students who like to do physical science is 15.
The number of students who like to do both is 7.
When we illustrate the information on a Venn Diagram, we can easily see that, 5 of the students do not like to do any of the labs.
The number of students who like to do chemistry labs but not physical science labs are those students who like only chemistry labs.
To find this, we subtract the number who like to do both labs from those who like to do chemistry labs.
This will give us, 19-7=12