The four instruments that are in the Orchestra are Bass, Cello, Violin, and Viola.
All four are in the Strings section. The other three sections are: Brass, Woodwinds and Percussion.
Two instruments in each would be:
Strings: Violin & Cello
Brass: Trumpet & French Horn (also Trombone and Tuba)
Woodwinds: Flute & Clarinet (also Oboe, English Horn and Bassoon)
Percussion: Snare, Tympany (plus a variety of other percussion instruments.
There are four instruments in an orchestra, violins, violas, cellos, and basses and they decrease in pitch respectivly. There are however, five sections. Violin I, violin II, viola, cello, and bass. There are some special pieces however that split other instruments into two sections.
At least two french horns, four trombones, four trumpets, and two tubas.
A chamber orchestra has the same instruments as a full orchestra, just reduced in numbers. There would be two to four cellos in most chamber orchestras.
An orchestra of all strings, Violins, Violas, Cellos and Basses. The Piano, being a member of the percussion family would not normally be part of the string orchestra unless being used as solo instrument.
The violin is the highest instrument in a string orchestra. The violins are divided into two sections (1st violins and 2nd violins), the 1st violins usually play the tune and play higher than the 2nd violins. However, the piccolo is the highest instrument in a full orchestra. The difference between a string orchestra and a full orchestra is that the string orchestra has only stringed instruments while a full orchestra has strings, woodwinds, brass, and percussion.
There are two main reasons. First is that percussion instruments are generally loud, and would cover up other sections. Second is that percussionists are often responsible for more than one part in a piece, and frequently have to be able to move from one instrument to another.
The main four bowed string instruments in the Romantic-Era orchestra include the Violin, of which there are two groups of sixteen and fourteen usually, the Viola, of which there are usually twelve, the Violoncello, otherwise known as the Cello, of which there are ten, and the Double Bass, of which there are eight. These numbers, however, vary depending on what time period in which the work in question was written.
One would be the Sousaphone.
It depends on the band. I'm assuming the "Concert Band" which is usually the same as the symphony orchestra - two from the oboe family (the oboe and English horn) and two from the bassoon family (the bassoon and the contrabassoon).
On the low end, there might be two horns and two trumpets. On the large end, there are four horns, three trumpets, three trombones (2 tenor, 1 bass), and a tuba. Some pieces, such as Mahler or Bruckner symphonies, use even more instruments than that.
Most orchestral music is written for 1st and 2nd violins, or two sections. Sometimes those parts might be divided further, but that doesn't count as separate sections.
In your heart, the top two hollow sections are called atrium and the lower two are ventricles.