Only in certain circumstances such as having your king in check with no squares to move to and the only way to stop the check is to capture the piece delivering the check.
Yes you can
plan to kill king
Yes, by that you capture a piece.
YES!!
anything but a king
Yes
Not at One Movement
yes
Chess is based off of war. Also it's just a habit.
A pawn can kill diangular foward or backwards
Yes , the queen can capture the king and this ends the game since the king's capture is the goal of the game of chess .
Absolutely, as long as it does not put the king in check.