Beginner Tactics - Why Isn't This Mate? I was playing on chesstempo and came across the following setup:

[FEN "k1r4r/p6p/5p2/3Q4/1R5P/PPqn4/3N1P2/1K1R4 b - - 1 1"]


With black to move. I was unable to solve this tactic - it seemed to me the best move was to place the queen on b2. In my mind this was mate. The queen is defended by the knight on d3 so the king could not escape.

However, the tactic said this was the wrong move. I ran it through chessbase and it was the same result.

Why is queen to b2 the wrong move here? The correct move was rook to c6, but I have no idea why.
1...Qb2 is not a legal move because black is in check; 1...Rc6 blocks the check. Another alternative to block the check is 1...Qc6, but that would drop the knight on d3.

[FEN "k1r4r/p6p/5p2/3Q4/1R5P/PPqn4/3N1P2/1K1R4 b - - 1 1"]

1... Rc6 (1... Qc6 2. Qxd3)