Answer
(a) NH4+
(b) H2CO3
(c) HBr
Work Step by Step
A conjugate base acquires a proton to produce its conjugate acid.
So, add H+ to each base. (Do not forget to balance charges.)
(a) NH3 + H+ → NH4+
(b) HCO3- + H+ → H2CO3
(c) Br- + H+ → HBr