What does this rebus mean?

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A chess tournament is taking place on knock-out terms (the one who loses the match is out of the game).
(a) If 10 matches are played in total, how many players participated?
(b) If 20 players took part in the tournament, how many matches were played?

I am a normal creature, but I have five hands. I can even have more but even then I will be considered normal.

Who am I?

I have one of the three numbers: 1, 2, or 3 in my mind. I speak only truth. You can ask me just one question for which I will only reply in yes or no or don't know. What question will you ask from me so that you are able to know the number?

Eight of us go fourth, not back, to protect our king from an attack. What are we?

A bomb exploded in a room full of married couples and no one died. How?

Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

A man was driving a black truck. His lights were not on. The moon was not out. A lady was crossing the street. How did the man see her?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

I look at you, you look at me, I raise my right, you raise your left. What am I?