Which is the strongest base?

Question

H2S, H2SO3, S2-, SO3(2-), PO4(3-) * choose one*

F-, NO2-, CNO-, HCNO, HF *choose one*

Answer 1

S2- for the first one, CNO- for the second.

Answer 2

which 1 has an OH(minus) to give off?

Answer 3

The weakest acid is the strongest base.  A base is a proton acceptor.  That would be PO4^3- for the first one.

HF Ka=6.8 x 10^-4

HCNO Ka = 3.5 x 10^-4

HNO2 Ka = 4.5 x 10^-4

Kb for F- = 1.5 x 10^-11

Kb for CNO- = 2.9 x 10^-11

Kb for NO2- = 2.2 x 10^-11

These are just about too close to call, but I would say CNO- if we had to pick.  But just a small difference in Ka from a different acid dissociation table could change the choice.