Answer:
Pure Water
Explanation:
The common ion effect describes the effect on equilibrium that occurs when a common ion (an ion that is already contained in the solution) is added to a solution. The common ion effect generally decreases solubility of a solute(Khan Academy).
NaCl, AgNO3, KCl, BaCl2 solutions all have a common ion with AgCl. As a result of this, AgCl will be much less soluble in these solvents than it is in pure water.
Therefore, AgCl will have the highest solubility in pure water compared to all the solutions listed above.
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[H_{3}O^{+}] = 0.00770 M
The equilibrium equation representing the dissociation of 

Given [H_{3}O^{+}] = 0.00770 M
Let the initial concentration of acid be x and change y
So y =
=
= 0.00770 M



0.00257 x - 0.00001979 = 0.00005929
x = 0.031 M
Therefore, initial concentration of the weak acid is <u>0.031 M</u>