Regarding exemption of Gratuity

Sir, I am an Accountant and filed a Income tax return of an employee who was servicing with an Ltd company, Sir in the asstt year 2019_2020 the assessee has received a sum of Rs 10.00 lac on account of gratuity, but the said amount of gratuity has been calculated by the department as taxable Income, sir I want to know that how many amount of gratuity is exempt from the income Thanks