Answer and Explanation for the First Question:
For the first question, when a 3.0 M aqueous NaOH solution is added to a neutral solution containing litmus, the color change in the solution would be from purple to blue. Thus, the answer would be C.
Litmus exists in solution in equilibrium form as H-Lit(aq) (red) ⇌ H⁺(aq) + Lit⁻(aq) (blue). At around pH 7, or neutral, the solution contains an equal amount of both forms of litmus, resulting in a purple color. This is because there are always some H⁺ ions present in the solution, even in neutral solutions, and the red and blue forms of litmus are present in equal amounts, which make the solution purple.
When a strong base like NaOH is added to the litmus solution, the OH⁻ ions from NaOH fully dissociate and react with the H⁺ ions in the litmus solution, forming water. This reaction causes the equilibrium position to shift in the direction of replacing the lost H⁺ ions. As more H-Lit(aq) molecules dissociate to form H⁺(aq) and Lit⁻(aq), the litmus becomes more ionized.
Since ionized litmus in solution is blue, the color of the solution will change from a neutral purple to a basic blue.
Answer and Explanation for the Second Question:
For the second question, according to the information given, the most likely pH of the solution is 6.0. Thus, the answer would be B.
The pH of the solution can be determined by looking at the color change of the three indicators added. Bromocresol green is yellow at the acidic end of its range, blue at the basic end of its range, and its pH range is 3.8 to 5.4. Chlorophenol red is yellow at the acidic end of its range, red at the basic end of its range, and its pH range is 5.2 to 6.8. Thymol blue is yellow at the acidic end of its range, blue at the basic end of its range, and its pH range is 8.0 to 9.6. Since the solution is blue when bromocresol green is added and orange when chlorophenol red is added, the pH of the solution must be between 5.4 and 6.8. The only possible value in this range is 6.0, which is why it is the most likely pH of the solution.