Missing question:
a) strong base and its conjugate acid.
b) weak base and its conjugate acid.
c) strong acid and strong base.
d) weak acid and its conjugate base.
e) weak acid only.
f) weak base only.
g) strong acid and its conjugate base.
Answers are:
b) weak base and its conjugate acid. For example weak base ammonia (NH₃) and its conjugate acid ammonium ion (NH₄⁺).
d) weak acid and its conjugate base. For example weak acetic acid (CH₃COOH) and its conjugate base CH₃COO⁻.
Buffer solution changes pH very little when a small amount of strong acid or base<span> is added to solution.</span>
