Answer: First option.
Step-by-step explanation:
Given two sets A and B, the union (A∪B) will be the set of elements which belong to either A or to B or to both.
Inf this case you have these two sets:
[tex]P=[/tex]{[tex]5, 6, 7, 8, 9[/tex]} and [tex]Q=[/tex]{[tex]1, 2, 3, 4, 5[/tex]}
To find the union of these sets, put together the elements of the set P and the elements of the set Q (you need to remember that no element must be repeated).
Then, you get that the union of sets P and Q is:
[tex]P[/tex]∪[tex]Q=[/tex]{[tex]1, 2, 3, 4, 5,6, 7, 8, 9[/tex]}
This matches with the first option.