At 298 K, the solubility of gases in water is influenced by their polarity and ability to form hydrogen bonds. Among the options:
- HCHO (formaldehyde): It is a polar molecule and can form hydrogen bonds with water, making it highly soluble in water.
- Vinylchloride: This compound is only slightly polar and does not form strong interactions with water, making it less soluble.
- Argon: This is a noble gas and is essentially non-polar, making it poorly soluble in water.
- CO\(_2\): While can CO\(_2\) dissolve in water, it forms weak interactions, and its solubility is lower compared to HCHO.
Thus, HCHO (formaldehyde) is the most soluble in water at 298 K.