Question

Why would `NaHO_4(s)` in solution turn red litmas paper blue?

Answer 1

It is acidic.

Explanation:

Red litmus paper turns blue under acidic conditions, so if `NaHO_4 (s)` in solution turns the litmus blue, has acidic properties.

I've never come across `NaHO_4 (s)` though. Are you sure it's not `NaHSO_4` which is an acidic salt?