Population because you are holding it
Since a hypothesis is a statement rather than a question, you could simply restate the line given to you in line 1. (That is of course your hypothesis is on the subject of people and social media.)
If I were to make a hypothesis off of that subject I would use something along the lines of:
"People who use social media more than others are more likely to struggle with social skills face to face."
Hope this helps! :)
