Sandy would reach an incorrect outcome.that's because she will repeat this mistake in the future too.
Gain 1.
This is because of Chlorine's placement on the periodic table. Chlorine is a Halogen, thus being located in group 17 or 7A. This means it is one of the closest elements to being a Noble Gas or group 18/8A.
Chlorine has 7 valence electrons, and in order for it to become a Noble Gas, it needs 8. Cl- is typically the symbol used to represent this as Chlorine needs to gain an electrons instead of lose; once Chlorine gains the electron, it will be stable.
This also means that Chlorine has a high ionization energy or, in simpler terms, it would be difficult to remove an electron from Chlorine.
Hope this helps!
To get the number of gold atoms, you have to divide the mass of the gold by the mass of the gold atom. It follows this simple equation

.
Let x be the number of gold atoms. Plug in the values to a calculator.
x =

Both have the same units so the unit gram(g) can be cancelled.
x then would be equal to 1.53x10^22. So there are 1.53x10^22 atoms of gold in 5 g of gold
If he was 30.8% too low, it means that he was at 69.2% of the boiling point needed. So 50o C is 69.2% of total.
In order to know what 100% is, you can divide the number by it's percentage and then multiply it by a hundred.
So: 50/30.8=1.623
1.623*100=162.3
So the correct boiling point of the liquid he was working with in the lab is 162.3 oC