who is better bishop or knight?

Pancakes.

They're different and yet for all the differences nearly equivalent -- Each one is to some degree better or worse depending on a specific position.

I think that a good question could be as follows.

---What is better, a pair ogf B`s or a pair of N`s?

and, in case you loose one piece, what would you prefer: A single N or a single B?

 yery excellent comment thnk u.

thanks for Tabor for his good comment.

Until you're looking at a specific position, or at least discussing a type of position it is pretty much meaningless.

Against a lone black king, I would much prefer a bishop pair to a knight pair!

King Bishop>Knight>Queen Bishop

The answer to this, along with the vast majority of plausible "which is better" questions, is this: It depends.

As to having pairs, I will take the bishops over a pair of knights, but a single knight or bishop depends on the position. In an opening if I must trade a bishop for a knight, I don't think twice about it.

But pancakes are ALWAYS better.

if i have a chance to trade a queen for 2 rocks,is it good?,or the queen is better? thanks.

^ it depends on the position. If it's closed, your rooks are useless. If it's open and you have plenty of minor pieces to support the rooks, they will be a match for the queen.

Usually, a bishop is slightly better.

In the midgame a bishop is usually better unless the position is closed or the bishop is weak.

In the endgame, a knight is usually better if the pawns are all on one side of the board, and a bishop is usually better if the pawns are on two sides of the board.  Of course it also matters whether the bishop is strong or weak.