In homologous series, the forth member has the chemical formula c4H9OH. the ninth member of the same homologous series has the chemical formula?

Homologous series is a group of organic compounds having same general formula or similar structure and similar chemical properties in which the successive compound differ by methylene group that is CH_2.
For eg, alkanes( methane CH₄, ethane CH₃CH_3, propane CH₃CH₂CH₃ and so on..)
alcohols(methanol CH₃OH, ethanol CH₃CH₂OH...

Fourth member of the series is C₄H₉OH, add CH₂ group for the next member of the series.
Thus, Fifth = C₅H₁₁OH
Sixth = C₆H₁₃OH
seventh = C₇H₁₅OH
eighth =  C₈H₁₇OH
ninth = C₉H₁₉OH