Final answer:
The riddle describes water, with its properties aligning with those of moisture in the air, and its molecular and phase characteristics. It plays a key role in weather phenomena and art but can be adverse for agriculture.
Step-by-step explanation:
The riddle you've presented describes a substance that is always moist, terrible for agriculture when excessive, but favored by artists, small but not too tiny, with particles that suspend finely, crystalline and visible yet problematic in clothes, and associated with humidity levels often represented on psychrometric charts, which sometimes use triangles with percentage markers. The answer to this riddle is water (C).
Water (H₂O) exists in three states: solid, liquid, and gas, which correspond to ice, water, and water vapor respectively. In our atmosphere, water droplets are found suspended, creating phenomena like fog and clouds - examples of colloidal systems where liquid water droplets are dispersed in the air. These droplets can aggregate around nuclei like dust particles or ice crystals and under the right conditions may fall as precipitation.
Artists often prefer the moist medium of water-based paints, which employ dispersion methods to distribute pigment particles evenly. In contrast, excessive moisture is detrimental to agriculture as it can lead to conditions that make soil less arable and increase the risk of crop diseases.