Answer: First option.
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:
{
} and
{
}
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:
∪
{
}
This matches with the first option.