Rules of Checkmate [duplicate]

Question

I’ve attached a picture of the board configuration of an end game. Black wins this game by checkmate, however, I’m wondering how this is valid checkmate?

To my understanding, checkmate occurs when a king is under threat of being captured and there are no other moves present on the board to prevent the king from being captured.

However, in this configuration, we can see that the f1 king is being attacked by the f2 queen. However, I’m wondering why the white king is unable to capture the f2 queen since technically the f6 rook is pinned against the black king and would not be able to capture the white king if it were to capture the queen.

Can anyone help me make sense of the rules?

[FEN "8/5pk1/3R1rp1/8/8/2Q4P/P4q2/5K2 w - - 0 1"]

Answer 1

White's king can only take the black queen if the king will not still be in check. Here is what the FIDE Laws of Chess say:

3.9.1 The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces, even if such pieces are constrained from moving to the square occupied by the king because they would then leave or place their own king in check.

So, no, the white king is not allowed to take the black queen and so it is checkmate.

Answer 2

To make sense of the rules, imagine that pieces pinned against the King can move, and the game is lost by the King who is captured first. Then the position that you show would continue 1.Kxf2 Rxf2 and the game would be over before White could play Qxg7. If you like, you can suppose that under some mediaeval system of honor, Kings do not permit themselves to be captured, but instead commit ritual suicide before that can happen.

CORRECTION Very stupidly, I first wrote "2.Qxg7 and the game would be over before Black could play ..Rxf1." @Rosie F pointed this out to me, and I am grateful and ashamed in equal measure. But the idea of "ritual suicide" does explain differently than just quoting FIDE rules.