TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The nanoparticle comprises a particle of a metal oxide selected from titanium oxide, aluminum oxide, or zirconium oxide. Preferred Process: The formation of a nanoparticle covered with the dispersant from a nanoparticle precursor is performed by an in-situ synthesis method. The nanoparticle is generated from the nanoparticle precursor by applying an energy to the nanoparticle precursor; or by irradiating the nanoparticle precursor with a microwave. The nanoparticle and the dispersant are brought into contact with each other while generating the nanoparticle having a small particle diameter by loosening a nanoparticle aggregate.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): Preparation of the phosphorus compound containing a nitrogen-containing aromatic heterocyclic cationic group involves reacting a compound of formula R1-Ar with a compound of formula X1-R2-B1-PO(OR3)(OR4).Ar=a nitrogen-containing aromatic heterocyclic group (preferably an imidazole group);andX1=a group capable of becoming an anion moiety of a protonic acid as X-.Preferred Medium: The dispersion medium comprises an organic compound (preferably a polymerizable organic compound). Preferred Definitions:    A+=imidazolium cation;    Y'=SO3 or PO2(OH);    B1=a single bond;and    Ar+=an imidazolium cation.    SPECIFIC COMPOUNDS - 16 Compounds are disclosed as (I) e.g. 3-(3-hexadecyl-1-imidazolio)-1-propanesulfonate (IA); 3-(3-hexadecyl-1-imidazolio)-1-propanesulfonic acid triflate; 3-(2-hexadecyl-1-pyrazolio)-1-propanesulfonate; 3-(2-hexadecyl-1-pyrazolio)-1-propanesulfonic acid triflate; and 3-(3-octyl-1-triazolio)-1-butane sulfonate.    EXAMPLE - N-hexadecylimidazole (12.3 g) was dissolved in acetone (80 ml), and the mixture was cooled in an ice-water bath. Into the resultant, a solution in which 1,3-propanesultone (5.13 g) was dissolved in acetone (80 ml) was dripped, and after the dripping was completed, the resultant was stirred at room temperature. After the completion of the reaction, the resultant was filtered to obtain a precipitate. The precipitate was dried under reduced pressure, to obtain 3-(3-hexadecyl-1-imidazolio)-1-propanesulfonate (M-1) (15.4 g). 3-(3-Hexadecyl-1-imidazolio)-1-propanesulfonate (0.20 g) was dissolved in 1-butanol (BuOH, 36 ml), and the mixture was cooled in an ice-water bath. Into the resultant, concentrated hydrochloric acid (5.8 ml) and TiCl3OH (concentration: 5.3 M, 3.4 ml) were each slowly dripped, thus a colorless transparent mixed liquid was obtained. The temperature of the mixed liquid was rapidly raised to 70 degrees C by using a microwave reactor while adjusting the output of the microwave at maximum of 30 W (0.7 W/cm3), and after the temperature became constant, the mixed liquid was irradiated with the microwave for 60 minutes. After being left to cool, a trace amount of white precipitate was removed, thus a titanium oxide (TiO2) nanoparticle dispersion liquid was obtained. Further, the dispersion medium was distilled off from the TiO2 nanoparticle dispersion liquid, thus a high-concentration TiO2 nanoparticle dispersion liquid was obtained. Still further, the high-concentration TiO2 nanoparticle dispersion liquid was dried under reduced pressure to obtain the nanoparticle/dispersant complex powder (test). Similarly comparative nanoparticle/dispersant complex powder were also prepared except that 0.16 g of dodecylbenzenesulfonic acid (DBSA) was used as the dispersant instead of M-1. By using the test and comparative nanoparticle/dispersant complex powders and BuOH high-concentration nanoparticle dispersion liquids were prepared. The results showed that the test/comparative liquid showed: transparency of A (i.e. no turbidity was observed apparently)/B (i.e. turbidity was possibly present); and coloring suppression of A (i.e. no coloring was observed apparently)/B (i.e. coloring was possibly present). Similarly, by using the test and comparative nanoparticle/dispersant complex powders and BuOH low-concentration nanoparticle dispersion liquids were prepared. In this case the test/comparative liquid showed: transparency of A/A; and coloring suppression of A/A.