The $\mathrm { p } K _ { a }$ Of Acetic Acid At

The $\mathrm { p } K _ { a }$ of acetic acid at $30 ^ { \circ } \mathrm { C }$ is _____, if its acid ionization constant is $3.2 \times 10 ^ { - 6 }$ .

A) 5.5
B) 2.7
C) 3.6
D) 4.8
E) 6.4