Puzzle: mate in one, while two natural queen moves stalemate
Published · By TG, the site operator
Today's note is a puzzle: White to move and mate in one. White has a queen and a king against a lone black king. Two queen moves look just as forcing as the mate, and both of them are draws.
The position in FEN is 8/8/8/8/8/1Q6/5K2/7k w - - 0 1. White has a king on f2 and a queen on b3. Black has only a king, on h1.
Before you open the answer
A game is drawn when the player to move is not in check and has no legal move. The FIDE Laws call this stalemate. If the move that creates it was legal, the game ends at once, so a win can be thrown away with one careless queen move. With a lone king on the board, every square it can reach matters.
Before you move, do two things. Count the squares the black king could step to. Then check each candidate: a checkmate needs both a check and no square left to run to.
Play a few moves against the computer and count the king's squares before each queen move →
Show the solution
1.Qh3# The queen slides along the third rank to h3 and gives check down the h-file. The king cannot go to h2, which the queen covers, and cannot go to g2 or g1, which the king on f2 covers. No piece can capture the queen, so it is checkmate.
Why not 1.Qg3? It takes away h2 and g2, and it looks like the net. But Black is not in check and has no legal move, so the game is a draw. 1.Qb8 also stalemates: the queen covers the diagonal to h2, and the king on f2 covers g1 and g2. Both drawing moves look restrictive, which is exactly the trap. A winning move has to leave the king a check to face.
How the answer was checked
The solution was checked by computer with the python-chess library. The script listed all 29 legal first moves for White. Exactly one of them, 1.Qh3, is checkmate. Two others, 1.Qg3 and 1.Qb8, leave Black with no legal move and no check, which is stalemate. The script is kept beside this note.
The same rule on this site
The board recognises stalemate automatically, and it treats the position as a draw, alongside threefold repetition, the fifty-move rule and insufficient material. The rules guide explains each of them, with a diagram for stalemate. Play a practice game and watch for the moment when the king has no square left: that is where a won ending turns into a draw.
Sources
- FIDE Handbook: Laws of Chess, Article 5.2.1 (stalemate) — FIDE
- Chess Play Online rules guide — Chess Play Online
- python-chess documentation — python-chess project
Written by the operator of this site from the sources listed above. Spotted a mistake? Email [email protected] and it will be corrected.