What is this reference material in spectrophotometry?
As the reference is the solvent alone, does it mean the samples are dilute solutions in water ? if so, how they solved benzene in water?


I come to a different conclusion.

To me it reads as follows:


sample: solution of benzene, acetone, acetonitrile, etc. in water
reference: water


Benzene is soluble in water: about $1.8\,\mathrm{g\cdot L^{-1}}$ at 25 °C.

Edit

As a reference (blank), a solution of everything except the sample is used. In organic (photo)chemistry this usually means: just the solvent. The situation is different in biochemistry, medicinal chemistry, etc. when complex aqueous buffer systems are used. Here, everything except the probe really means that the whole buffer is used as a blank.