Answer
$i$
Work Step by Step
We know that $i^{2}=-1$. Therefore, $i^{4}=i^{2}\times i^{2}=-1\times-1=1$.
We can use the fact that $i^{4}=1$ in order to evaluate higher powers of $i$.
$i^{25}=i^{24}\times i=(i^{4})^{6}\times i=(1)^{6}\times i =1\times i =i$