What is an element in science​

Which statement about the stamps is correct?

Ionic compounds are made of ions, and yet the overall charge of an ionic compound is neutral. why?

Which of the following natural processes is most likely to support the formation of an underwater sinkhole? a pollution buildup from deposited minerals b limestone cave collapsing due to changes in sea level c erosion of large amounts of sand moved by ocean waves d oxidation of rock formed by chemical weathering