The correct answer is option C) 7.

pH is a measure of the acidity or alkalinity of a solution. It is a logarithmic scale that ranges from 0 to 14, where pH 7 is considered neutral. Solutions with a pH less than 7 are acidic, while solutions with a pH greater than 7 are alkaline.

When NaCl is dissolved in water, it dissociates into Na+ and Cl- ions. These ions do not react with water to produce any acidic or basic species. Therefore, the solution of NaCl is neutral and has a pH of 7.

However, there is an important factor to consider in this question - the temperature. The question states that the temperature of the solution is 85°C. At higher temperatures, the autoionization of water can slightly affect the pH of the solution.

At 25°C, the autoionization of water is given by the equation:
2H2O ⇌ H3O+ + OH-
At this temperature, the concentration of H3O+ and OH- ions are equal, resulting in a neutral pH of 7.

However, at higher temperatures, the equilibrium shifts towards the production of H3O+ ions. This means that the concentration of H3O+ ions increases and the pH decreases slightly.

In this case, at 85°C, the concentration of H3O+ ions in the solution is higher than the concentration of OH- ions, resulting in a slightly acidic solution. However, the question specifically asks for the pH of the solution, which is a measure of the concentration of H3O+ ions. Since the concentration of H3O+ ions is still extremely low and the solution is still considered neutral, the pH of the solution remains 7.

In summary, the pH of an aqueous solution of NaCl at 85°C should be 7 because even though the solution is slightly acidic due to the autoionization of water at higher temperatures, the concentration of H3O+ ions is still extremely low and the solution is still considered neutral.