The second statement, "Because junk food is bad for your health, the size of sodas offered at fast-food restaurants should be regulated by the federal government," can be argued and proven with evidence in an argumentative essay.
This statement presents a clear claim and outlines a specific action (regulating soda sizes) that can be debated. It also allows for the use of evidence related to health impacts of junk food, governmental roles in public health, and existing regulations to support the argument.
The first statement, "Junk food is bad for your health," is more of a declarative claim and is less suitable as a thesis for an argumentative essay because it doesn’t specify a course of action or a clear argumentative stance. It can be supported by evidence but does not present an argument that can be debated outright.