It is a compound composed of sodium (Na) and chloride (Cl)
An isotope is when an element has the same number of protons and different number of neutrons. That is why the atomic mass changes.
Answer: 300mm
Explanation:
30cm x (10mm/1cm) x <em>(1mm/1mm)</em> = 300mm
<em>Btw, I'm not sure about the </em><u><em>(1mm/1mm).</em></u>