The volume of the cube is:
\[
\text{Volume of cube} = \text{edge}^3 = 8^3 = 512 \, \text{cm}^3
\]
The area of the base of the vessel is:
\[
\text{Area of base of vessel} = 12 \times 20 = 240 \, \text{cm}^2
\]
Let the rise in the water level be \( h \). Using the formula for volume:
\[
\text{Volume of water displaced} = \text{Area of base of vessel} \times \text{height of water rise}
\]
\[
512 = 240 \times h
\]
Solving for \( h \):
\[
h = \frac{512}{240} = 2.13 \, \text{cm}
\]
Thus, the correct answer is \( 2.13 \, \text{cm} \), but this option is not available, so the correct answer is (d) None of these.