There are four syllables in this word : ob-ser-va-tion
Nest is only one syllable.
No, you do not divide a one-syllable word. The word is pronounced with a single stress point.
The word plant has one syllable. This means that there is no syllable divide for this word.
Grim-ace, divided as "grim" (1 syllable) and "ace" (1 syllable).
tooth
Fin/ish
colo-ring
re-treat
of-ten
Rob-in
a-bol-ish
east-ern