Gravitational force becomes (stronger/weaker) as mass increases

Stronger ... becasue gravitational force is force pulling all matter (anything that has mass and occupies space). The more the matter (which also includes mass), the more the gravitational force.

So, the answer is stronger.

Well Babygirl123 the gravitational force would increase or become stronger as the mass of a planet say Earth increases. while as a little planet such as Pluto has a little to no amount of gravitational force.