Pension of a widow

What is the treatment of the pension received by the widow of the central govt employee, the details of the case are employee died in the year of 2007, but due to some legal problems she received the pension in 2011 the sum of pension from the death of her husband. How the pensionis taxable, is it taxable in year wise i.e, taxable in the relevant assessment years at the rates applicable in that assessment year or at the time of receipt at the applicable slab rates ?