King can't move to b3 square. It's protected by the bishop on f6. That's why it's a stalemate
Why game draw by stalemate?
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Stalemate means that the King is not checked, but any move he makes results in an illegal move (moving the king in which is captured next turn). The queen prevents any move on the A column, the rook prevents any move on the 5th row and C column which cannot be taken since the bishop is guarding it. The king's only remaining legal move is moving to b3, but that cannot happen since the bishop on f7 is protecting that square. Since the king has no remaining legal moves and is not being checked (hence the term "checkmate") the king cannot move, resulting in a draw.
If the king can move a B3 without being captured. Why does it say game draw by stalemate?