The spelling of the word "Riusah" can be explained using the International Phonetic Alphabet (IPA). The first sound in "Riusah" is /ɹ/, which is represented by the letter "r". The second sound is /i/, which represents the long "e" sound and is represented by the letter "i". The third sound is /u/, which represents the "oo" sound and is represented by the letter "u". The final sound is /sə/, which is represented by the letters "sa". Therefore, the correct spelling of "Riusah" is as follows: /ɹi'juːsə/.