Pick the odd one out from the following, also give reasons.
(a) amoeba, sponge, hydra, frog
(b) snail, slug, squid, snake

a) sponge because only sponges are non-motile out of the four.
b) Snake because only snakes belong to the phylum chordates while all others are non chordates i.e. belong to the phylum mollusca.