Should industries releasing heavy metals into land and water ecosystem be penalized

State one important difference between a physical change and a chemical change?

The chemical formula for emerald is be3al2(sio3)6.an emerald can be decided as

An unknown substance is a white solid at room temperature and has a melting point of 78 °c. which of the following substances is most likely to be the identity of the unknown sample? a. naphthalene, a molecular solid with the formula c10h8 b. silica, a network solid held together by covalent bonds with the formula sio2 c. calcium chloride, an ionic compound with the formula cacl2 d. water, an molecular compound with the formula h2o