I generally create 5 Partitions(/, /boot, /opt, /home, Swap) to install Ubuntu 16.04. I Want to save my data of /home and /opt/lampp while formatting again. I do it now by taking backup in Other Disks.
Is there any other way to take backup in system without any other disk.
Is there any other way to take backup in system without any other disk while I am logged in my system with a bootable USB.
Their is no need to take backup in another disk.
I your case you have allocated a partition home. If you only erase and install existing Ubuntu (root partition) home will be untouched. so if you copy the files in home it will be safe.
Just select erase and install Ubuntu over existing Ubuntu.
After re installation, you can mount existing home partition as in the below article.
https://help.ubuntu.com/community/Partitioning/Home/Moving
For this you have should have same username.