Suzane took a piece of paper and then folds it into a paper airplane. She throws it at her little brother.
He is a naughty boy and responds by ripping up the paper. Is it a physical change or a chemical change? Give a reason for your answer.
 Ripping up the paper.
 

Three days when it rained continuously, Akash covered his bicycle with a polythene sheet, whereas his friends just did not bother to do the same to their cycles! Few days later Akash’s friends noticed that their cycles had some brown powdery patches on it where Akash’s seemed to be new.

(b) Which metal is used in making a bicycle? What happened to Akash’s friend’s bicycle? Why did the metal develop reddish-brown patches?