Recitative: Speech-like, the text is more (if not completely) syllabic than melismatic like in arias (typically, not always), and use of some rubato to elongate or quicken phrases, tries to mimic speech pattern (inflection) to an extent
Harmonically loose (may cadence/modulate unexpectedly and 'faster' than in aria).
speeds the story along (re-read after reading aria).
typically chordal arpeggiated accompaniment
typically precedes a respective aria. (is before a aria, in an opera).
Aria: a mix of syllabic (1 note/syllable) neumatic (2-4notes/syllable) and melismatic (+4 notes/syllable). (More notes per syllable).
the 'memorable part' (a melody versus being based on speech/inflection)
where the recitative speeds the plot along, the aria is where a singer takes time to reflect on a particular emotion/situation.
Versus the unstable recitative, arias of the Baroque era typically written as Da Capo arias. (A type of ternary form, ABA, written out AB with a 'da capo al fine' (from the top to the 'fine' (specified end), at the end of the A section. The 2nd time the A is sung, the singer would typically embellish the A section with ornamentations.
example: Purcell's 'Dido and Aeneas': "Thy hand Belinda!...... When I am laid..."
The first part 'Thy hand Belinda!' is the recitative.
The second 'When I am laid...' is the aria. Listen to the recitative, and the aria will immediately follow it.
Edit: Forgive me Mamimanka, or don't ;).
Although, this would amount to 1-2 questions on a test. If you can't figure out the answers yourself you'll still fail. So 'dyoh' (do your own homework').