What of the following ko values represents the weakest base?

The weakest base corresponds to the highest ( K_b ) value. However, if you're looking for the weakest base in terms of ( K_a ) values, you would want the lowest ( K_a ) value for its conjugate acid. In general, a base with a lower ( K_b ) indicates a weaker base. If you provide specific ( K_b ) values, I can help determine which one represents the weakest base.