Question: Alexander Borodin was part of a group of 19th century composers that were known as what "number"?

Context paragraphs:
Spidertown, Ontario: Spidertown was a small, agricultural supply and services based community in southwestern Ontario, Canada that existed in the last half of the 19th and the early 20th century.  The site of the former hamlet is located at the present intersection of Mount Carmel Drive, Blackbush Line and Salem Road, on the boundary between the current municipality of North Middlesex and the municipality of South Huron.  Little is currently known of Spidertown's founding, nor the origin of its name.  The hamlet is described in one source as consisting, at one point in time, of "taverns on both corners" and "four homes".  It is known, that in the latter 19th century a general store was operated in the community by Alexander Todd, presumably the same individual who operated two other general stores during the period at Maguire and Moray as well.  A medical doctor, T. L. Flaherty, maintained a practice in a corner house in the hamlet in the latter 19th century, but is known to have moved his office to Mount Carmel, 2 km to the east, before 1898.  It is believed that Spidertown began to go into decline because of its inability to compete economically with the nearby hamlet of Mount Carmel.  Spidertown is recorded as having disappeared by 1914.

History of the Irish language: The history of the Irish language begins with the period from the arrival of speakers of Celtic languages in Ireland to Ireland's earliest known form of Irish, Archaic Irish, which is found in Ogham inscriptions dating from the 3rd or 4th century.  After the conversion to Christianity in the 5th century, Old Irish begins to appear as glosses and other marginalia in Latin manuscripts, beginning in the 6th century.  It evolved in the 10th century to Middle Irish.  Early Modern Irish, otherwise known as Classical Irish, was a literary language that represented a transition between Middle and Modern Irish.  It was used by writers in both Ireland and Scotland until the 17th century, in the course of which slowly but surely writers began writing in the vernacular dialects, Ulster Irish, Connacht Irish, Munster Irish and Scottish Gaelic.  As the number of hereditary poets and scribes dwindled under British rule in the early 19th century, Irish became a mostly spoken tongue with little written literature appearing in the language until the Gaelic Revival of the late 19th century.  The number of speakers was also declining in this period with monoglot and bilingual speakers of Irish increasing adopting only English: while Irish never died out, by the time of the Revival it was largely confined to the less Anglicised regions of the island, which were often also the more rural and remote areas.  In the 20th and 21st centuries, Irish has continued to survive in Gaeltacht regions and among a minority in other regions.  It has once again come to be considered an important part of the island's culture and heritage, with efforts being made to preserve and promote it.

Pyotr Ilyich Tchaikovsky and The Five: In mid- to late-19th-century Russia, Pyotr Ilyich Tchaikovsky and a group of composers known as The Five had differing opinions as to whether should be composed following Western or native practices.  Tchaikovsky wanted to write professional compositions of such quality that they would stand up to Western scrutiny and thus transcend national barriers, yet remain distinctively Russian in melody, rhythm and other compositional characteristics.  The Five, made up of composers Mily Balakirev, Alexander Borodin, César Cui, Modest Mussorgsky, and Nikolai Rimsky-Korsakov, sought to produce a specifically Russian kind of art music, rather than one that imitated older European music or relied on European-style conservatory training.  While Tchaikovsky himself used folk songs in some of his works, for the most part he tried to follow Western practices of composition, especially in terms of tonality and tonal progression.  Also, unlike Tchaikovsky, none of The Five were academically trained in composition; in fact, their leader, Balakirev, considered academicism a threat to musical imagination.  Along with critic Vladimir Stasov, who supported The Five, Balakirev attacked relentlessly both the Saint Petersburg Conservatory, from which Tchaikovsky had graduated, and its founder Anton Rubinstein, orally and in print.

Ballet (music): Ballet as a music form progressed from simply a complement to dance, to a concrete compositional form that often had as much value as the dance that went along with it.  The dance form, originating in France during the 17th century, began as a theatrical dance.  It was not until the 19th century that ballet gained status as a “classical” form.  In ballet, the terms ‘classical’ and ‘romantic’ are chronologically reversed from musical usage.  Thus, the 19th century classical period in ballet coincided with the 19th century Romantic era in Music.  Ballet music composers from the 17th–19th centuries, including the likes of Jean-Baptiste Lully and Pyotr Ilyich Tchaikovsky, were predominantly in France and Russia.  Yet with the increased international notoriety seen in Tchaikovsky’s lifetime, ballet music composition and ballet in general spread across the western world.

Twelve-tone technique: Twelve-tone technique—also known as dodecaphony, twelve-tone serialism, and (in British usage) twelve-note composition—is a method of musical composition devised by Austrian composer Arnold Schoenberg (1874–1951) and associated with the "Second Viennese School" composers, who were the primary users of the technique in the first decades of its existence.  The technique is a means of ensuring that all 12 notes of the chromatic scale are sounded as often as one another in a piece of music while preventing the emphasis of any one note through the use of tone rows, orderings of the 12 pitch classes.  All 12 notes are thus given more or less equal importance, and the music avoids being in a key.  Over time, the technique increased greatly in popularity and eventually became widely influential on 20th century composers.  Many important composers who had originally not subscribed to or even actively opposed the technique, such as Aaron Copland and Igor Stravinsky, eventually adopted it in their music.

Classical music of the United Kingdom: Classical music of the United Kingdom is taken in this article to mean classical music in the sense elsewhere defined, of formally composed and written music of chamber, concert and church type as distinct from popular, traditional, or folk music.  The term in this sense emerged in the early 19th century, not long after the United Kingdom of Great Britain and Ireland came into existence in 1801.  Composed music in these islands can be traced in musical notation back to the 13th century, with earlier origins.  It has never existed in isolation from European music, but has often developed in distinctively insular ways within an international framework.  Inheriting the European classical forms of the 18th century (above all, in Britain, from the example of Handel), patronage and the academy and university establishment of musical performance and training in the United Kingdom during the 19th century saw a great expansion.  Similar developments occurred in the other expanding states of Europe (including Russia) and their empires.  Within this international growth the traditions of composition and performance centred in the United Kingdom, including the various cultural strands drawn from its different provinces, have continued to evolve in distinctive ways through the work of many famous composers.

The Mighty Handful: The Mighty Handful (Russian: Могучая кучка ), also known as The Five and The New Russian School, were five prominent 19th-century Russian composers who worked together to create a distinctly Russian classical music.  Mily Balakirev (the leader), César Cui, Modest Mussorgsky, Nikolai Rimsky-Korsakov and Alexander Borodin all lived in Saint Petersburg, and collaborated from 1856 to 1870.

Alexander Borodin: Alexander Porfiryevich Borodin (Russian: Алекса́ндр Порфи́рьевич Бороди́н ; ] , 12 November 183327 February 1887) was a Russian Romantic composer of Georgian origin, as well as a doctor and chemist.  He was one of the prominent 19th century composers known as The Mighty Handful, a group dedicated to producing a uniquely Russian kind of classical music, rather than imitating earlier Western European models.

Anatoliy Brandukov: Anatoly Andreyevich Brandukov (Russian: Анато́лий Андре́евич Брандуко́в ) (January 6 [O.S. December 25, 1858] 1859 – February 16, 1930) was a Russian cellist who premiered many cello pieces of prominent composers including Pyotr Tchaikovsky and Sergei Rachmaninoff.  Born as Russian classical music was flourishing in the middle of the 19th century, he worked with many of the important composers and musicians of the day, including performances with Anton Rubinstein and Alexander Siloti.  As a soloist, he excelled in performance and was especially noted for stylish interpretations, his refined temperament, and beautiful, expressive tone.  In his later years, he became a professor at Moscow Conservatory, and continued to perform well into his later life.  Although his popularity is obscured by the more famous composers and virtuosos, his influence on those composers' most prominent compositions is evident.

Russian Easter Festival Overture: Russian Easter Festival Overture: Overture on Liturgical Themes (Russian: Светлый праздник, "Svetliy prazdnik" ), Op.  36, also known as the Great Russian Easter Overture, is a concert overture written by the Russian composer Nikolai Rimsky-Korsakov between August 1887 and April 1888.  It was dedicated to the memories of Modest Mussorgsky and Alexander Borodin, two members of the group of composers known in English as "The Five".  It is the last of what many call his three most exceptionally brilliant orchestral works, preceded by "Capriccio Espagnol" and "Scheherazade".  The work received its premiere at a Russian symphony concert in St. Petersburg in late December 1888.

Supporting paragraphs: Alexander Borodin The Mighty Handful
Answer: The Five