<prompt> The gold standard for diagnosis of gastroesophageal reflux disease GERD is:Barium swallowEndoscopy24-hours pH monitoringEsophageal manometry  <response>: Barium swallow- IOC for diagnosis of Hiatus hernia and Zenkers diveicula Endoscopy Biopsy- IOC for diagnosis of Barrets esophagus 24 hours PH monitoring- Gold standard Investigation for GERD Esophageal manometry- IOC for diagnosis of motility disorders of esophagus like Achalasia cardia, Diffuse esophageal spasm and Nut crackers esophagus. 