Question

H3PO4(aq)+NH3(aq)←−→NH4+(aq)+H2PO4−(aq)

a. base H3PO4 conjugate base H2PO4− ; acid NH3 conjugate acid NH4+
b. base H3PO4 conjugate acid H2PO4− ; acid NH3 conjugate base NH4+
c. acid H3PO4 conjugate acid H2PO4− ; base NH3 conjugate base NH4+
d. acid H3PO4 conjugate base H2PO4− ; base NH3 conjugate acid NH4+

Answer 1

d. acid H3PO4 conjugate base H2PO4− ; base NH3 conjugate acid NH4+
The rule is : acid donates the proton, forming the conjugate base, and the base accepts the proton, forming the conjugate acid.