Question

what does firmness mean?
able to be firm
the state of being firm
without being firm
in a firm way

Explanation:

The word "firmness" is a noun, and it refers to the state or quality of being firm. "Able to be firm" is about capability, "without being firm" is the opposite state, and "in a firm way" is an adverb - like description. The state of being firm best defines "firmness".

Answer:

the state of being firm