The reason KBR is neutral is because when reacting with H2O you form, KOH and HBR, hence they cancel each other out, and you are left with a neutral pH of solution of 7, nothing contributed to the pH of pure water. CsF is basic because when reacting with H2O, it forms CsOH and HF, which is a strong base and a weak acid, meaning that the pH will be higher than 7, which indicates a basic solution.