If it is located at the second to last row of the periodic table (the halogen family), has seven electrons on it's outer shell, and has an oxidation number of -1, it is a halogen.
Hope this helps : D
Answer: It is called a Crookes Tube, and he used it to discover cathode rays, which were later determined to be electrons.
The 2nd one I believe
Answer- 2nd
Covalent bonds and it is between the hydrogens (hydrogen bonds)