An organic compound $\left({\mathrm{C}}_8{\mathrm{H}}_{10}{\mathrm{O}}_2\right)$ rotates plane-polarized light. It produces pink color with neutral ${\mathrm{FeCl}}_3$ solution. What is the total number of all the possible isomers for this compound?

Since compound ${\mathrm{C}}_8{\mathrm{H}}_{10}{\mathrm{O}}_2$ corresponds positively to neutral ${\mathrm{FeCl}}_3$ hence it will be a phenolic compound the possible structures which are optically active are as followed

Hence, total optically active isomers will be $6$.