ANSWER
C) 0.21 %
EXPLANATION
We have that the account pays 2.5% interest per year.
A year consists of 12 months.
So to find the monthly interest, we have to divide it by 12.
That is:
[tex]\begin{gathered} \frac{2.5}{12}\text{ \%} \\ =\text{ 0.2083 }\cong0.21\text{ \%} \end{gathered}[/tex]The monthly rate is 0.21%