1. The problem statement, all variables and given/known data tetrahydrothiophene is stronger acid than tetrahydrofuran 2. Relevant equations Acidic strength depends on stability of conjugate base.And stability of conjugate base in turn depends on following factors resonance,inductive effect,hybridization,atomic size i.e electron density and electronegativity. 3. The attempt at a solution As electronegativity of oxygen is greater than sulphur ,tetrahydrofuran should give more stable conjugate base after removal of acidic hydrogen.,But my teacher says electron density plays bigger role in determining stability of conjugate base than electronegativity .So,sulphur in tetrahydrothiophene is bigger than oxygen in size that's why it will have less electron density that's why will give more stable conjugate base .Hence tetrahydrothiophene more stable than tetrahydrofuran.Right?