What black piece can you capture? This is homework from school.
[FEN "8/8/2n5/1p6/4r3/1Kb5/3p4/8 w - - 0 1"]
This question needs some context. All the pieces are black. In order to capture, a piece of an opposing color needs to occupy the square of the captured piece. The king can not be captured, only placed in checkmate or stalemate.
Since there are no opposing piece, one correct answer could be
none of the pieces.
If the question supplies a white piece and location, then the question can be answered. For example if it was white to move, and there was a white bishop on d3 and a white king on d5 then the question would have some educational value for a beginning student. What captures could be made in that situation?
If we make the following two assumptions
Then clearly the only piece the king is adjacent to is the bishop, so that must be the piece. However, this bishop appears to be protected by the pawn. This must not be the case, because the bishop is the only possible piece to capture. Thus we can conclude the bishop is not on C3, but rather F6 and the board is simply inverted.
So the game continues
1) kxf6 e8=Q 2) kg7 rd6 3) kh7 ng5+ 4) kg7 qf7++