<prompt> ___ of Fluid is required to produce costophrenic angle bluting on erect chest X-ray, in cases of pleural effusion:100ml300ml500ml750ml  <response>: At least 100ml of fluid is required to detect by USG.A minimum of 300ml is required to produce bluttening of costophrenic angle on erect chest X-ray.About 500ml of effusion is required for detection on clinical examination. 