A reasonable pka for a weak base is:

10.3

0.9

5.8

7.4

13.1

0.9

Explanation:

The pka represents the force by which the molecules need to dissociate for the acids,

Hence, lower the pka stronger will be the acid and that therefore will dissociate completely and vice versa, for a weak acid higher the pka.

And in case of a base, it will be completely reversed, lower pKa, weaker base,

and higher pKa, stronger base.

From the data of the question,

0.9 is the lowest value of the pKa, hence, weakest base.