Thanks you sir.
Basic definition is:Change in length/original length.So change in length is 2l.And original length is l.So it becomes 2.While the correct answer to this statement is 1.
The CHANGE in length. So, what is the final length? 2I. What's the initial? I.
CHANGE = FINAL LENGTH - INITIAL LENGTH
2I is not the change. Keep that in mind and try the equation again. See what you get.