what do you mean by this last term of cloud?
It is a type of interstellar cloud, the density and size of which permit the formation of molecules,
Molecular cloud
s a type of interstellar cloud, the density and size of which permit the formation of molecules, most commonly molecular hydrogen (H). 
what is the estimate time of the formation and evolution of the solar system? It began 4.5 billion years ago is there any proof or model which justifies its formation? Yes, it's called the nebular hypothesis who gave this hypothesis? Emanuel Swedenborg, Immanuel Kant, and Pierre-Simon Laplace what was stated in it, can you give at least one point? It says that the Solar System formed from the gravitational collapse of a fragment of a giant molecular cloud.
wiki:25697159
Molecular cloud [SEP] Introduction
A molecular cloud, sometimes called a stellar nursery (if star formation is occurring within), is a type of interstellar cloud, the density and size of which permit the formation of molecules, most commonly molecular hydrogen (H). This is in contrast to other areas of the interstellar medium that contain predominantly ionized gas. Molecular hydrogen is difficult to detect by infrared and radio observations, so the molecule most often used to determine the presence of H is carbon monoxide (CO). The ratio between CO luminosity and H mass is thought to be constant, although there are reasons to doubt this assumption in observations of some other galaxies.