Carbon dioxide gas has a solubility of 0.0972 g/100 g h2o at 40 degrees celsius. expressed in parts per million, this concentration is closest
(1)0.972 ppm (2)9.72 ppm (3)97.2 ppm (4)972 ppm

Ppm is a value that represents the part of a whole number in units of 1/1000000. It is dimensionless quantity, a ratio of 2 quantities of the same unit. The easiest way to do these is to remember the conversion that 

0.0972 g/100 g H2O = 0.0972/100 mL = 0.972 g/L = 972 mg/L = 972 ppm