Final answer:
The most reasonable pH for a 0.015 M NaOH solution is 12.18. This was calculated by finding the concentration of hydronium ions [H3O+] via the water ion-product constant and then taking the negative logarithm to find the pH.
Step-by-step explanation:
The question concerns calculating the pH level of a sodium hydroxide (NaOH) solution. Because NaOH is a strong base, it ionizes completely in water, resulting in an equal concentration of hydroxide ions [OH-]. For a 0.015 M NaOH solution, this is also the concentration of [OH-].
Firstly, we can determine the concentration of hydronium ions [H3O+] using the ion-product constant for water (Kw) at 25 °C, which is 1.0 x 10^-14. The formula to calculate [H3O+] from [OH-] is:
[H3O+] = Kw / [OH-]
Given [OH-] is 0.015 M:
[H3O+] = 1.0 x 10^-14 / 0.015 = 6.67 x 10^-13 M
Next, we calculate the pH using the formula:
pH = -log [H3O+]
pH = -log(6.67 x 10^-13) = 12.18
Based on this calculation, the most reasonable pH for a 0.015 M NaOH solution would be option 4) 12.18.