What mass of solid naoh would be needed to make 645 ml of freddy's naoh solution?

NaOH reacts with KHP 1:1 molar ration

Molar mass KHP = 204.227 g/mol

1.126g = 1.126 / 204.227 = 0.00551 mol KHP

You require 0.00551 mol NaOH

Molar mass NaOH = 40g/mol

0.00551mol = 0.00551*40 = 0.221g NaOH

Answer: Dissolve 0.221 g NaOH in 645 ml solution and this will exactly neutralize 1.126 g KHP.