4. More people bought 1 cupcake than any other number of cupcakes is the true statement.
Explanation;
First, we need to understand what each statement means and check if it's right by checking with the dot plot.
Statement 1; Every person bought at least one cupcake. This is not true as 2 people who did not buy any cupcakes at all. So statement 1 is not true.
Statement 2; The most cupcakes a person bought was 8. According to the dot plot, the most cupcakes bought by a person were 5 so statement 2 is incorrect.
Statement 3; Every person bought between 1 and 5 cupcakes. As said for statement 1 not everyone who came bought a cupcake so statement 3 is incorrect.
Statement 4; More people bought 1 cupcake than any other number of cupcakes. According to the dot plot, 8 people bought 1 cupcake and no other number of cupcakes were bought as much. So this is the right statement.