The elements are arranged by atomic mass. Before, they were arranged by atomic mass.
Answer:
a.
Explanation:
Writing 2NaCl as Na2Cl2 completely changes the molecule.
2NaCl describes two different molecules, each having one Sodium atom and one Chlorine atom.
Na2Cl2 describes one single molecule made up of two Sodium atoms and two Chlorine atoms
A thin gold foil .
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