An ion is an atom with a net electric charge due to the loss or gain of one or more electrons.
An isotopeis each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties.
Not 100% sure, but I'd have to say this:
When rounding for sig figs, you look at the other numbers in your calculation and see which one has the least amount of sig figs. This number is 2.70. (3 sig figs). So, you round to 3 significant figures in your calculation.
Hope this helped!
