Query regarding scientific equipment

Rupisha Agarwal (31 Points)

29 December 2020  
One of my client deals in scientific equipment and he was supplies scientific and research equipments to DRDO..According to AAR and notification the concessional gst rate has charged 5% instead of 18%.
He received exemption certificate from DRDO but when he purchased the same equipment then he was paid the duty @ 18%.
So what is the treatment while filing GST return and ITC.