What piano grade is Etude Op 10 No 4?
umm...you're level is grade 9 rcm, and you want to learn Op. 10 No. 4,seriously, I would'nt reccomend it at this level. Secondly, you should talk to your teacher 1st, she will know whether you are ready for chopin etudes.
Which Chopin Etude is the easiest?
The 25/12 is rather an "Easier" one and often is the first Chopin etude many students play. Throughout many years I've been discussing those etudes with quite a few pianists who not only recorded them all, but also played them live and everyone tends to agree.