Re: what is the experiment that leads to the discovery of quark?

In answer to your three questions:

How does the experiment of the isolation of electron from an atom leads to 
the discovery of quarks?

I'm not sure I understand the questions. "Isolating" electrons from atoms
produces ions (electrically charged atoms) in a process called ionization.
This process is not directly used to search for quarks.

what is the experiment that leads to the discovery of quark?

Quarks were discovered in 1968 at SLAC by Jerome Friedman, Henry Kendall
and Richard Taylor, for which they won the Noble Prize in 1990.  
In their experiment they bounced electrons off protons (Hydrogen atom
nuclei). If the proton was a point-like particle, the electrons would be
deflected in a very specific way. However, they observed that the electrons
were not deflected in a manner consistent with a point-like proton. James
Bjorken and Richard Feynman analyzed their data and found that the
scattering of the electrons was consistent with a proton consisting of
quarks. 

A free quark has never been observed conclusively, despite extensive
experimental efforts. They have only been in observed in bound states
called mesons (a quark and anti-quark) and baryons (three quarks). Protons
and neutrons that make up nuclei are baryons, while the meson carry the
residual strong force that binds the nucleus together. 

For a brief overview of the history of particle physics and the discovery
of particles, see http://ParticleAdventure.org

What is an eV?

eV is an abbreviation for electron-Volt. It is a unit of energy, similar to
everyday energy units such as joule and calories but much smaller. Particle
physics deals with very small energies, so it makes sense to use a unit
that denotes small energies. The eV unit also simplifies many of the
calculations that particle and nuclear physics require.

An eV is defined as the amount of energy an electron gains when it is moved
across a potential difference of 1 Volt. You can find a detailed
explanation in most college-level freshman physics text, such as 
Serway or Halliday and Resnick. 

Hope this helps,

Reyco Henning