[raha]

Do you know if we add alkali to parared will its spectrum change?if yes how?

[ARGOS++]

Dear Raha,

Para Red is the “Coupling”-Product of p-NitroAniline with β-Naphtol
As you may know, that β-Naphtol like Phenol is acting as a middle strong Acid, so you can build with Alkali the corresponding Salt, containing the Naphtolat-Ion.
In Para Red this functional Group is still left intact.

So what you have to find out is, of what kind of an Effect Naphtolat ( ØØ-O^─ ) and the –O-H of Naphtol  are, and which is of the stronger Nature.
Hint: The Sign of the Effect is not relevant for the introduced Change in Colour, but its Strengt.
If you identify the Naphtolat as the stronger Effect, then a so called “Bathochrome” Effect for the resulting Colour must result.
A “Bathochrome” Effect is the same as a “Red-shift”, or a Shift in the Direction of longer Wavelengths. The contrary is called “Hypsochrome” Effect.

Can you find the very small Piece of the Answer left to you?

Good Luck!
                    ARGOS⁺⁺