Question

what is the disadvantage in comparing line segment by Mere observation​

Answer 1

Answer:

When we compare two line segments of almost same lengths we can't be sure about line segment of greater length therefore it is not appropriate method to compare line segments having a slight difference between their lengths.

Answer 2

$\red \bigstar$Answer:-$\red \bigstar$

On comparing the lengths of line segments by mere observation the difference may not be obvious for all the pairs of line segments.