Dear Prashant,
Any death cum retirement gratuity received by Central and State Govt. employees, Defense employees and employees in Local authority shall be exempt u/s 10
In other cases if received by legal heirs then it is taxable under "income from other sources", since it is taxable under other sources where assesse has an option to offer his income to tax either on receipt basis or on accrual basis..
Therefore it is upto the assessee in which year it is to be taxed but exemption u/s 10 upto Rs, 3.50 lacs is available only in the year of receipt, therefore it should be offer to tax in FY 2010-2011 so that Exemption u/s 10 can be claimed