Answer:
The concentration of chloride ion is 
Explanation:
We know that 1 ppm is equal to 1 mg/L.
So, the
content 100 ppm suggests the presence of 100 mg of
in 1 L of solution.
The molar mass of
is equal to the molar mass of Cl atom as the mass of the excess electron in
is negligible as compared to the mass of Cl atom.
So, the molar mass of
is 35.453 g/mol.
Number of moles = (Mass)/(Molar mass)
Hence, the number of moles (N) of
present in 100 mg (0.100 g) of
is calculated as shown below:

So, there is
of
present in 1 L of solution.
A) Mass Number
B) Protons and Electrons
C) (I think group but I'm not 100% sure on this...)
D) 12 (To work out the number of neutrons you do MASS number - ATOMIC number aka the number of protons so in this case you'd do 23-11=12)
Hope this helps