Revenue Secretary Hasmukh Adhia has said that fixing the GST rate, deciding on exempt items and ensuring no dual control by the Centre and states, are among the seven key challenges which have to be overcome before GST can be rolled out by Ist April next year.<br/><br/>Mr. Adhia listed seven challenges which include: calculation of revenue base of Centre and states and compensation requirements, structure of GST rates, list of exemptions, forming of consensus on Model GST Bill, threshold limits, compounding limits and cross empowerment to mitigate ill-effects of dual control.