Why do some objects reflect light while some let light pass through them?

[ARAVIND113122]

i've read that some molecules release absorbed photons in the opposite direction[causing reflection] while some release it in the original direction[making the object transparent]...what molecular factors decide this phenomenon?why do some objects reflect?why are others transparent?

 

[Drakkith]

See these articles:
http://en.wikipedia.org/wiki/Transparency_and_translucency
http://en.wikipedia.org/wiki/Reflection_(physics)