It would be the Aqueous solution
<span> N-16
</span>7 protons & 9 neutrons
<span>7 + 9 = 16
</span>
You did not include the statements but since magnesium chloride is ionic substance that we know that magnesium and chlorine formed an ionic bond. Therefore your statement most likely will talk about how one magnesium atom gave up 2 electrons while two chlorine atoms took 1 electron. The reaction looks like Mg+2Cl⇒MgCl₂.
I hope this helps. Let me know in the comments if anything is unclear.
Explanation:
Let us assume that total mass of the solution is 100 g. And, as it is given that acetic acid solution is 12% by mass which means that mass of acetic acid is 12 g and 88 g is the water.
Now, calculate the number of moles of acetic acid as its molar mass is 60 g/mol.
No. of moles =
= 
= 0.2 mol
Molarity of acetic acid is calculated as follows.
Density = 
1 g/ml = 
volume = 100 ml
Hence, molarity = 
= 
= 2 mol/l
As reaction equation for the given reaction is as follows.

So, moles of NaOH = moles of acetic acid
Let us suppose that moles of NaOH are "x".
(as 1 L = 1000 ml)
x = 20 L
Thus, we can conclude that volume of NaOH required is 20 ml.