ANSWERS: 2
• The mass (weight) of an atom is based on it's number of protons (forgetting about neutron isotopes... and electron are leptons, so they can kiss my *ss). Number of protons define which element an atom is, therfore: Different elements have different weights. Now size is a tricky one: the size of the atom is defined by the space taken up by the forces exerted by the electrons in the outermost shell (because they're all just empty space anyway). Because different shells can only hold so many electrons, as your number of protons increases on the periodic table... and so therefore do your electron increase (because it's an atom, not an ion), then after a certain count, the shell fills up, putting electrons in the next shell out, making... a bigger atom. So yes, some atoms are bigger than others. But what's a "big" atom anyway? They're all freakin' tiny. I'm going with: A) Different sizes and Different weights. Teacher doesn't like it, send 'em here. I'll school 'em good.
• The other guy knows way more than I do but I suspect your teacher is going for same size, different weights. As Anon. says, the name of the element is determined by the number of protons, which also determines the weight (ignoring neutrons for the moment). The weight change is significant; the change in size is either nonexistent or very small. ~ If you want the smart answer, go with the other guys' (anon's). I think my answer is the simpler, more obvious one.

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