my son is doing his 12th standard in commerce, can he get admission in BITS for BE in mechanical engineering

Dear, For appearing BITSAT one has to complete +2 with PCM with an average of 75% and not less than 60% in any of the physics/chemistry/Math. As your son is doing with commerce in +2 - I 'm sad for saying-- No. Wishing best for your son in future in his own domain.