When a certain aqueous solution is diluted, its conductivity decreases but its pH remains constant.

The solution could be

A ethanoic acid
B sodium chloride
C sodium hydroxide
D nitric acid.


please explain?

(fairly sure) B, sodium chloride.
Not a chemistry expert, but my reasoning is this:
For the PH to remain constant, the substance must be neither an acid nor a base , ie,
Have a ph of 7, the same as water.
NaCl, is a salt, a reaction of an acid and a base.
The rest are either explicitly acids, or (sodium hydroxide) a base.
Now, it states it is AQUEOUS , already in water.
We all know salt increases the conductivity of water.
Adding more water reduces the NaCl:water ration, decreasing conductivity.