Why is this the best move?

Hi,

The engine shows this as a blunder and says that the best move is Qxb1+

Why is that, given the Knight would have taken my Queen afterwards?

Thank you

Ok, well firstly the engine analyzed to depth 10, which means you basically asked a learning disabled child for chess advice.  Change your settings immediately, depth 10 isn't even sufficient for beginners.  Beginners can certainly get by with depth 20, which takes stockfish all of seconds.  I prefer a little deeper, but it isn't truly necessary except for advanced players.  

Second, its obvious that black's position is completely borked, and after qa5, the engine's recommendation of bxd7 followed by e6, without analyzing it, just looks like the start of a winning attack.  This is what engines do.  They recommend crazy looking moves if their calculations show you are less screwed.  Here, taking the rook isn't actually so crazy looking, since you get a rook and then the bishop for the queen.  Its easy to see that haul being better than retreating the queen and facing a devastating attack.  Black is toast either way, but you likely "blundered" in the computer sense of not selecting the least-terrible option.  

Yeah 5+3 vs 9 is not such a bad exchange. But to an untrained eye the Queen's move doesn't really look like blunder.

Thank you

Computer engines are designed to play the "best move" at a certain depth, which either leads to an evaluation as high as possible (in a winning position) and as small the magnitude as possible (in a losing position).

That bishop on b5 is nasty, so 26...Qxb1+ is probably the lesser evil.

Having seen lots of such queen losses, I have sacrificed queens more often than before in such manners, with mixed results.

the comp is right. if Qa5 ur opp cld play Bb6 trapping ur q

Different vision at different depth.

Although a beginner has difficulty in seeing a trapped queen at move 1, computers easily see that beyond move 10. 

Stockfish see more than one way to take down a trapped queen.

1. Bb6 ( cost white two minor pieces for one queen)

2. Bxd7 +( mentioned in your display).( cost white one minor piece). And Stockfish chose the second method as the better choice.

Thanks all for the comments!

1.Bb6 Qxb6 2.Bxd7+ wins the Q

1.Bxd7+ Kxd7 2.Bb6 Qxa4 doesn't win the Q

how does black get m8ed?