Dear Sir,
Arrears are taxable when they are actually received i.e. on receipt basis. We usually take salary income on actual basis because TDS liability on employer is on payment basis.
1) For F.Y. 2016-17, file ITR-1 showing the total salary of 8 months along with the bank interest income. Also to avoid mismatch with the Form 26AS and notices from the deptt. in future, file ITR with 8 month's salary only.
2) For F.Y. 2017-18, take total salary of 12 months along with arrears for filing ITR.