The correct answer is C. light.
Optically active 2-octanol is a chiral molecule, which means that it is not superimposable on its mirror image. This chirality is due to the presence of a chiral carbon atom, which is a carbon atom that is bonded to four different groups. When optically active 2-octanol is exposed to light, the chiral carbon atom can undergo a process called racemization, which is the process of converting a chiral molecule into a racemic mixture. A racemic mixture is a mixture of equal amounts of the two enantiomers of a chiral molecule. Enantiomers are molecules that are mirror images of each other but are not superimposable. When optically active 2-octanol is racemized, it loses its optical activity.
Dilute acid and base do not cause optically active 2-octanol to lose its optical activity. Humidity does not cause optically active 2-octanol to lose its optical activity.