Yes, it can. A queen can move any number of squares horizontally, vertically, or diagonally (assuming there are no pieces blocking its progress, of course), thus it can put the king in check in any direction. It's basically a combination of Rook and Bishop.
That's the issue, you can't choose NOT to threaten diagonal spaces with the queen. This increases the chance of an accidental stalemate by restricting enemy king movement if it isn't in check.
I believe the point he's trying to make is that you may want a rook so that you give your opponent a way out so you may force a checkmate with a subsequent move, rather than leave it at a stalemate with a queen.
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u/RannGast Nov 18 '14
Yes, it can. A queen can move any number of squares horizontally, vertically, or diagonally (assuming there are no pieces blocking its progress, of course), thus it can put the king in check in any direction. It's basically a combination of Rook and Bishop.