Concept:The instrument shown is a Secchi disc, which measures water clarity or turbidity.
Explanation:A Secchi disc is lowered into a body of water until it disappears from view.
The depth at which it becomes invisible indicates the transparency or turbidity of the water.
This method is used in oceans, lakes, rivers, and ponds.
Therefore, the factor being measured is a property of water, not of air, land, or grass.
Answer:B. in water
