All the air is removed in a sealed metal can. after the air has been removed, the can looks as if it were crushed. why?

The can looks like it was crushed because the outside pressure (aka atmospheric pressure) is pressing against the can that has no air in it, which is also called a vacuum in chemistry terms. The main thing to focus on is the atmospheric pressure that is pressing against the can and in the process, crushes it.

halogen, any of the six nonmetallic elements that constitute group 17 (group viia) of the periodic table. the halogen elements are fluorine (f), chlorine (cl), bromine (br), iodine (i), astatine (at), and tennessine (ts).

protocol for imps extraction focusing on membrane protein extraction, solubilisation, and purification.