The litmus paper test is used to identify if a solution is acidic or basic, it works by interacting with the solution and changing its color according to the pH of the solution, if the paper turns red, this means we have an acidic solution, and if the paper turns blue, this means that we have a basic solution.
In our question the only acid present is HNO3, so this will be the only one to turn the litmus paper red
NaOH is a base
AgNO3 and CaCl2 both are salts.
