When to regard water as a strong base
Question:

Classify each of the following ions according to whether they react with water to give a neutral, acidic, or basic
solution:
As a general rule:

Strong acid + Strong base $\rightarrow$ Neutral solution


Strong acid + weak base $\rightarrow$ acidic solution


Weak acid + Strong base $\rightarrow$ Basic solution


That's not true. The only time in which these rules are true is when you have an equimolar concentration of the acid and base in question, and the acids and bases must both be monoprotic and monobasic, or diprotic and dibasic, etc. Otherwise there are too many variables to consider for these guidelines to always ring true. Consider mixing 1.0 molar $\ce{H2SO4}$ with 0.10 molar $\ce{NaOH}$ ... I guarantee you that the pH of that solution is not &quot;neutral.&quot;

d) $\ce{K(H2O)6+}$ is the conjugae base of a weak acid, therefore the soltuion is basic.

I didn't know that potassium hydrated to a significant extent in water; even so, what the solution manual has written down is not the conjugate base of hydrated potassium cation - the weak acid.

However, all these answers imply that water is acting as a strong
base. How is this possible when water pH is $\sim 7$?

How do these answers imply that water is acting as a strong base?
Also regarding how water can be a strong base in general - it just depends on your solvent system.