Explain the following:
$(i)$ Why is it difficult to walk on marshy land?
$(ii)$ Why does an air-filled balloon rise up slightly when punctured from below?
$(iii)$ Why does a swimmer push water backward with his hands in order to swim in the forward direction?

(N/A) $(i)$ It is difficult to walk on marshy land because when we push the ground with our feet,the ground is soft and yields,failing to provide an equal and opposite reaction force as per Newton's third law.
$(ii)$ When an air-filled balloon is punctured from below,the escaping air exerts a downward force. According to Newton's third law,the air exerts an equal and opposite upward reaction force on the balloon,causing it to rise slightly.
$(iii)$ According to Newton's third law of motion,for every action,there is an equal and opposite reaction. When a swimmer pushes the water backward (action),the water exerts an equal and opposite force on the swimmer in the forward direction (reaction),which helps the swimmer move forward.