Question: Étude in C-sharp minor was written by the Russian symbolist composer Alexander Scriabin for which instrument?

Context paragraphs:
Piano Concerto (Scriabin): The Piano Concerto in F sharp minor, Op.  20, is an early work of the Russian composer Alexander Scriabin (1872–1915).  Written in 1896, when he was 24, it was his first work for orchestra and the only concerto he composed.  Scriabin completed the concerto in only a few days in the fall of 1896, but did not finish the orchestration until the following May.  It premiered on October 23, 1897.

Mystic chord: In music, the mystic chord or Prometheus chord is a six-note synthetic chord and its associated scale, or pitch collection; which loosely serves as the harmonic and melodic basis for some of the later pieces by Russian composer Alexander Scriabin.  Scriabin, however, did not use the chord directly but rather derived material from its transpositions.

Clavier à lumières: The clavier à lumières ("keyboard with lights"), or tastiera per luce, as it appears in the score, was a musical instrument invented by Alexander Scriabin for use in his work "".  However, only one version of this instrument was constructed, for the performance of "Prometheus: Poem of Fire" in New York City in 1915.  The instrument was supposed to be a keyboard, with notes corresponding to colors as given by Scriabin's synesthetic system, specified in the score, However, numerous synesthesia researchers have cast doubt on the claim that Scriabin was a synesthete.

Étude in C-sharp minor, Op. 2, No. 1 (Scriabin): Étude in C-sharp minor, Op.  2, No. 1, is an étude for piano, written by Russian composer Alexander Scriabin in 1887.

Étude in D-sharp minor, Op. 8, No. 12 (Scriabin): Étude in D-sharp minor, Op. 8, No. 12, is an étude for piano composed by Alexander Scriabin in 1894.  It features many technical challenges, including treacherous stretches with intervals up to an eleventh, numerous jumps in the left hand, repetitive chord strikes, and abundant octaves.  It is a particular favorite among pianists and audiences alike.  This piece was a favorite encore of Vladimir Horowitz.

Alexander Scriabin: Alexander Nikolayevich Scriabin ( ; Russian: Алекса́ндр Никола́евич Скря́бин , ] ; 6 January 1872 [O.S. 25 December 1871] – 27 April [O.S. 14 April] 1915 ) was a Russian composer and pianist.  Scriabin, who was influenced early in his life by the works of Frédéric Chopin, composed works that are characterised by a highly tonal idiom (these works are associated with his "first stage" of compositional output).  Later in his career, independently of Arnold Schoenberg, Scriabin developed a substantially atonal and much more dissonant musical system, which accorded with his personal brand of mysticism.  Scriabin was influenced by synesthesia, and associated colours with the various harmonic tones of his atonal scale, while his colour-coded circle of fifths was also influenced by theosophy.  He is considered by some to be the main Russian Symbolist composer.

Studies on Chopin's Études: Studies on Chopin's Études is a set of 53 arrangements of Chopin's études by Leopold Godowsky.  (The number of studies is often given as 54, with Op. 25, No. 2 having one study written as a considerably different ossia of another; a similar ossia also exists for one of the studies on Op. 25, No. 3, so the total number of studies can be taken to be 55.  In contrast, Godowsky's original numbering scheme runs only to 48.)  They are renowned for their technical difficulty: critic Harold C. Schonberg called them "the most impossibly difficult things ever written for the piano."  Several of the studies (for example, the study "Ignis Fatuus" on Chopin's Étude in A minor, Op. 10, No. 2) put the original right-hand part into the left hand; several others are for the left hand alone (for example, the study on the "Revolutionary" Étude, transposed to C-sharp minor).  Two of the studies even combine two études; the most well known of these, called "Badinage," combines both the G-flat (the "Black Key" Étude of Op. 10 and the "Butterfly" étude of Op. 25).

Étude Op. 25, No. 7 (Chopin): Étude Op. 25, No. 7 in C-sharp minor is a solo piano technical study composed by Frédéric Chopin in 1834.  Markedly different from Chopin's overall scheme of technical virtuosity, this étude focuses instead on perfect sound and phrasing, particularly for the left hand.

Prometheus: The Poem of Fire: Prometheus: The Poem of Fire, Op. 60 (1910), is a symphonic work by the Russian composer Alexander Scriabin for piano, orchestra, optional choir, and clavier à lumières or "Chromola" (a color organ invented by Preston Millar, in fact rarely featured in performances of the piece, including those during Scriabin's lifetime).  "Prometheus" is only loosely based on the myth of Prometheus.  A typical performance lasts about 20 minutes.

Julian Scriabin: Julian Aleksandrovich Scriabin (born Yulian Aleksandrovich Schloezer; Russian: Юлиа́н Алекса́ндрович Скря́бин , 12 February 1908 – 22 June 1919) was the youngest son of Russian composer Alexander Scriabin and Tatiana de Schloezer.  He was himself a promising composer and pianist, but he died at the age of eleven in mysterious circumstances.  In the last year of his life he wrote four preludes in his father's style, the authorship of which is questioned by some researchers.  Those preludes were published for the first time 95 years after his death by Edition Octoechos.  Musicologists have described Julian Scriabin both as a successor of his father and as an early representative of the early Russian and Soviet avant-garde of the 1920s.

Supporting paragraphs: Étude in C-sharp minor, Op. 2, No. 1 (Scriabin) Alexander Scriabin
Answer: piano