Answer :

I'm not sure how many reasons you want, but here are 3 reasons. 
1. Frogs can breathe on land and in water, whereas tadpoles can only breathe in water.
2. Frogs can go on land, and tadpoles cannot.
3. Tadpoles do not have limbs, frogs do.
frog can go on land 
tads can't breathe in and out of water, while frogs can 
Frogs have legs and arms tads do not
Frogs can make a noise tads can't
tads have gills frogs have lungs
tads have fins and frogs don't
tads change into frogs, but a frog stays a frog