Simichrome polish is the cat's meow on chrome.
Mother's products are very good.

As far as magnesium, if you've got it you would know already.

To differentiate aluminum and chrome, it's mostly the color. Aluminium is, shall I say, a bit "whiter" than chrome. Also, it gets chalky when it oxidizes. Chrome tends to get rust specks, or an orange tarnish.

Coated metals tend to be trim pieces.