By looking at the acceleration of the object.
In fact, Netwon's second law states that the resultant of the forces acting on an object is equal to the product between the mass m of the object and its acceleration:

So, when static friction is acting on the object, if the object is still not moving we know that all the forces are balanced: in fact, since the object is stationary, its acceleration is zero, and so the resultant of the forces (left term in the formula) must be zero as well (i.e. the forces are balanced).
I am almost sure it it (c)
The answer is group 18.
Explanation:
Group 18 is known as the Noble Gases. They are the most stable elements because they have a full outer shell of valence electrons, so they have no need to bond with other elements.