Arrear of salary

Arrears of salary received by an employee are taxed in the year of receipt if the same were not taxed earlier on due basis.However a relief can be claimed u/s 89 if it is taxed on receipt basis for the F.Y. in which it is received.

Yes arrear of salary amount is taxable in the year of received that amount.

It is taxable in the year of receipt if the same were not offered for assessment earlier years to which it belongs. 

However rebate u/s 89 is available on filing of form 10E