I do not understand how to do this questionScreenshot 2024-04-17 220652.png
Ammonia is a base and concentrations of ammonia is important for pH calculations. Here pH is determined by calculation of [OH-] by making rice table and using Kb value.
Kb = [OH-][NH4+]/[NH3]
[OH-]= Kb[NH3/[NH4+]
so as decreases also decreases and pOH increases and hence pH decreases.
So B is the right option.