Answer
a) Less than 7
b) Greater than 7
c) Equal to 7
d) Greater than 7.
Work Step by Step
a) Given the equal concentration and volume of the weak acid and the strong base, the mixture is at the equivalence point, so $pH = pKa < 7$
b) Given the equal concentration but higher volume of the weak base compared to the strong acid, the mixture is before the equivalence point so $pH > pKa$ for ammonium $pKa > 7$
c) Mixture of strong acid and strong base, volume x concentration is the same for both, it's at the equivalence point $pH = 7$.
d) Mixture of strong acid and strong base, same volume but the base is more concentrated, it's after the equivalence point $pH>7$
