Number of isomeric compounds with molecular formula$\mathrm{C}_9 \mathrm{H}_{10} \mathrm{O}$ which (i) do not dissolve in NaOH (ii) do not dissolve in 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__________.