Income Tax on Arrear Commutation Amount

Seems to be salary arrears, as commutation pension amount is generally paid in single slot,

It is not salary arrears, when I retire at that time some negotiation talks going on in between bank and IBA which is materialized later after my retirement. As a result my basic changed and the commutation amount which I got previous increased and I get salary arrear and commutation arrear as well. My question is about the second one commutation arrear and for that I asked here. Surprisingly the details of the credit also shows " XI Bipartite Commutation arrear".

This commutation amount would be taxable under head IFOS, and not tax-free.

You can claim relief under section 89 for tax deducted on arrear salary by filing form 10E