Step-by-step Solution:

\[ \textbf{Given (unsigned binary): } 10101.10101_2 \] \[ \begin{aligned} \text{Integer part }(10101_2) &= 1\cdot 2^4 + 0\cdot 2^3 + 1\cdot 2^2 + 0\cdot 2^1 + 1\cdot 2^0 \\ &= 16 + 0 + 4 + 0 + 1 = 21 \\[6pt] \text{Fractional part }(.10101_2) &= 1\cdot 2^{-1} + 0\cdot 2^{-2} + 1\cdot 2^{-3} + 0\cdot 2^{-4} + 1\cdot 2^{-5} \\ &= \frac{1}{2} + 0 + \frac{1}{8} + 0 + \frac{1}{32} = \frac{16+4+1}{32} = \frac{21}{32} = 0.65625 \end{aligned} \] \[ \therefore\quad 10101.10101_2 = 21 + \frac{21}{32} = \frac{693}{32} = \boxed{21.65625} \]