Answer:
C. increase to 7.
Explanation:
Hello,
In this case, the undergoing chemical reaction is:

Thus, the molar relationship is 1 to 1, therefore, the moles are:

Thus, since the entire hydrogen ions are neutralized, the pH C. increase to 7.
Best regards.
Before proceeding, we should write the reaction equation to better understand what is happening:
2AgNO₃ + Na₂S → Ag₂S + 2NaNO₃
Now, we may apply the law of conservation of mass, due to which the total mass before a chemical reaction is equivalent to the total mass after a chemical reaction. Therefore:
Mass of silver nitrate + mass of sodium sulfide = mass of silver sulfide + mass of sodium nitrate
Mass of silver nitrate + 156.2 = 595.8 + 340
Mass of silver nitrate = 779.6 grams