Tax on pension arrears

My father retd. Central Govt. Employee aged 85 years is getting a pension of Rs. 38100/-, This month he got Rs. 1,10,000/-  as arrears due to pension revision.

Please inform whether this shall be added to his current financial year's Income for calculation of I/Tax. If so his income will cross Rs. 5 lac limit pl. suggest remedies to avoid tax payment