The main difference difference ponds and lakes is that ponds

The difference is actually a result of the the depth. Ponds, according to limnology (the study of water bodies) are shallow enough where plants could conceivably grow across the entire surface. ... As a result, there are some very small bodies of water, less than an acre that are deep enough to be called lakes.

14,16 18 reacts with group

a corroding iron, if that's one of your choices