Number of isomeric compounds with molecular formula $\mathrm{C}_{9} \mathrm{H}_{10} \mathrm{O}$ which (i) do not dissolve in $\mathrm{NaOH}$ (ii) do not dissolve in $\mathrm{HCl}$. (iii) do not give orange precipitate with 2,4-DNP (iv) on hydrogenation give identical compound with molecular formula $\mathrm{C}_{9} \mathrm{H}_{12} \mathrm{O}$ is ____________.