Sodium hypochlorite is best described as:

Sodium hypochlorite is best described as a liquid form of chlorine that comes in various strengths. This compound is commonly used in water treatment processes, particularly for disinfection due to its effectiveness in killing bacteria, viruses, and other pathogens. The concentration of sodium hypochlorite can vary, which allows it to be applied in different scenarios based on the required strength for effective disinfection.

In understanding the other options, it's important to note that sodium hypochlorite is not a gas; chlorine gas is a different form entirely. It is also not a solid compound; while some chlorine compounds are solid, sodium hypochlorite is specifically a liquid. Additionally, sodium hypochlorite is not used solely for disinfection; it has a variety of other applications, including bleaching processes and odor control. Thus, the description of sodium hypochlorite as a liquid that comes in various strengths accurately captures its characteristics and uses.