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The pair of molecules which forms the strongest intermolecular hydrogen bonds is formic acid \(HCOOH\), and acetic acid \(CH _3 COOH\). A hydrogen bond is the electrostatic attraction between polar molecules that occurs when a hydrogen \(( H )\) atom bound to a highly electronegative atom such as nitrogen \((N)\), oxygen \((O)\) or fluorine \((F)\) experiences attraction to some other nearby highly electronegative atom.