The first chair violin was watched by other members of the orchestra for the keeping of the beat when a conductor was not present or could not be seen.
violin
writing
There is no guitar in a standard symphony orchestra. If the orchestra is playing a guitar concerto, the guitarist would sit in front of the orchestra, near the conductor, as would any other soloist.
the piano
The Piano
By numbers, it's the string section. A full-sized orchestra has around 60 string players
The piano and the violin were the most popular solo instruments used in the concerto of classical period. The violin was one of the most popular for the baroque period, and the increase in popularity of the piano caused that this instrument replaced the former. See http://au.encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761553032
For one thing, "string instruments" and "stringed instruments" are not the same. String instruments are the viol family and stringed instruments are any instrument that has strings. The piano and harp both qualify.Now, the piano is a percussion instrument that has strings and the harp is an unbowed stringed instrument.
By numbers, second place goes to the violas.
Mozart composed in every form of the time, but he probably composed the most for the orchestra.
The violin is probably one of the most important classical instruments. In the orchestra, the violins lead most of the melody, and the main violinist is second to the conductor in rank. As a solo instrument, it's also pretty important because it has a wide variety of notes and sounds.
The most popular musical instrument used in classical music compositions is the violin, with the piano also being widely used.