Final answer:
In the nineteenth century, the piano was significantly enhanced by extending its range to a full seven octaves, which contributed to its prominence in Romantic music.
Step-by-step explanation:
During the nineteenth century, the piano underwent significant changes due to the Industrial Revolution. One of the key features added to the piano was the increase in the range of notes it could play. Pianos evolved from having limited octaves to a full seven-octave range, allowing for a greater breadth in musical expression and complexity. This expansion in range helped the piano become the central instrument of Romantic music, marking a shift from the more limited harpsichord of previous eras.