Question

Please help with 18, 19 and 20

Answer 1

18, 19, and 20 are absurdly written questions, written by someone who is unclear on the concepts.  These three questions have no logical answers, and are terribly misleading for students who are trying to learn this stuff.

I haven't had the guts to review the other 12 questions on the sheet.  But really, the sheet should be shown to somebody in a higher position in the Science department of your school system.  This kind of material should be unacceptable in an educational setting, except once a year, on April 1.