Phthalic acid will dissolve 18g of per 100mL of boiling water.

(25g/18g) x 100mL = 138.89mL of boiling water is needed to dissolve 25g of phthalic acid.

yes it is

Para-phthalic acid" is not a commonly recognized chemical compound or term. It seems like there might be a misunderstanding or a typographical error in the name you're referring to. If you have a different chemical or substance in mind, please provide the correct name, and I'd be happy to provide information about it

180g/L in hot water

Phthalic anhydride is slightly soluble in methanol. But beware! In this case, phthalic anhydride will actually react with its solvent. This is called estrification of the anhydride. Methanol will break the ring of Phthalic anhydride and make an ester.

C6H4(CO)2O + CH3OH --> C6H4(CO2H)(CO2CH3)

Similarly, you might THINK Phthalic anhydride is soluble in water, but it actually reacts with water to make phthalic acid.

If you want to make a true solution of phthalic anhydride, I would recommend acetone, or methylethyl ketone.