opposite, before and infront of

Sanjay, this one is a bit difficult to answer. These words carry several different meanings -- the context is important to deciding what meaning applies.  Because you include "in front of", I'm assuming the context is positional.

"Opposite" can mean something that is the reverse -- "the opposite of black is white".  When used to describe a position or direction, "opposite" means "on the other side of".  "The market is on the opposite side of the street from the church." However, the street (or plaza, or river, or ....) is often implied and not spoken or written. "The market is opposite the church." You  need to make sure the implied relationship is understood.  "Go three blocks to the main plaza. There, opposite the church, you will find the market."

"Before" can relate to either time or position. When speaking of position, "before" and "in front of" have the same meaning. While "opposite" conveys an objective relationship between two objects (that is, the church is always opposite the market no matter the position of the speaker), "before" and "in front of" conveys a subjective relationship.  The position of the speaker or reader is important.  "Go three blocks to the plaza. You will see the market before you. If you turn around and face the church, the market will be behind you."

I hope I've answered your question.