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Answer: A. Na only
Sodium is an alkali metal, and chlorine is a halogen. This means that sodium contains one electron in its outer orbital and chlorine contains seven electrons in its outer orbital. One electron moves from the sodium atom and attaches to the chlorine atom to fill its outer orbital. This is the creation of two ions (sodium Na+ and chloride Cl-) and the result is table salt.
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Na+ is called a cation because it goes to the cathode if a current is passed through a solution containing this ion. Likewise, chloride is an anion (goes to the anode).
Andy, don't listen to these fools, they couldn't explain chemistry to anyone who doesn't already understand it with these ridiculous explanations, so I'll lay it out for you.
On the periodic table you'll notice that Sodium is on the far left and Chlorine is on the far right, but second to last column. The last column is where the noble gases are found, and they are called that because they're unreactive, basically too "fancy" to bond with any elements. (There are exceptions, but none you'll have to worry about for a long while!)
Now, the column with the noble gasses is the 8th column, because we skip all the metals that don't start until later on. I won't get into quantum mechanics, but that's how we know the elements in the 8th column have their outer, bonding (valence) shell filled with 8 electrons. All of the atoms strive to have 8 electrons in their outermost valence shell either by stealing them or by sharing them.
Stealing electrons happens by the 1st and 7th groups on the periodic table, because the seventh group just needs 1 more electron to have 8 and the first row has a full shell underneath its outermost shell with one in it, so if it gives it away, it's more stable. The reason bonding happens is because electrons are negative. See, the sodium gives up its electron to chlorine and they're no longer neutral anymore. The chlorine has a negative charge and the sodium now has a positive charge. They then attract to each other similar to how a magnet does.
This is a general idea that you can apply to a lot of elements in the first two columns, and I can try to explain more if anyone has any questions or if I've left something unclear.