According to context clues which best defines the underlined word gaseous

There is no context here, but gaseous is an adjective describing the gas-like quality of a substance.  For example, pure oxygen is gaseous at room temperature.  

answer: the first one

explanation:

explicitly is defined as “in a clear and detailed manner, leaving no room for confusion or doubt.” the rest are interpretive and not clearly proven leaving in fact possible “confusion or doubt” which explicitly, by definition cannot have.

can you give me a hint