What can be seen in traces?

TRACES is a web-based application of the Income Tax Department that provides an interface to all stakeholders associated with TDS administration. It enables viewing of challan status, downloading of Conso File, Justification Report and Form 16 / 16A as well as viewing of annual tax credit statements (Form 26AS).

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     what is the process of deducted TDS in the arrear salary?

TDS deducted gets reflected in 26AS (available with TRACES), and its the assessees' capital, which he/she can claim against its tax liability. If no tax liability, it can be claimed as refund.