A minor

A composition for an organ that incorporates a hymn tune is known as a chorale prelude.

Take your pick! Extant forms when Bach began composing included the Prelude, the Fugue, the Chorale Prelude, the Toccata, several concertante forms, and so on. Bach raised all of them to their highest peak. There is no one best answer, but the "safe" answer is probably "Chorale Prelude".

The final work Bach completed was a chorale prelude for organ, dictated to his son-in-law, Johann Altnikol, from his deathbed. Entitled Vor deinen Thron tret ich hiermit (Before thy throne I now appear, BWV 668a). Source: http://en.wikipedia.org/wiki/Bach

The first year in the list of Bach's compositions is 1700.

Three titles are catalogued:

- Christ, der du bist der helle Tag - Organ Works - BWV 766

- O Gott, du frommer Gott - Organ Works - BWV 767

- Sei gegruesset, Jesu guetig - Organ Works - BWV 768