How to make XP as the default O.S with grub2 ?

Soln:-

1) give the following command :- grep -i XP /boot/grub/grub.cfg

you will get the o/p in the following lines

menuentry "Windows XP Professional x64 Edition (on /dev/sda2)"

2) now give the command sudo gedit "Windows XP Professional x64 Edition (on /dev/sda2)" and change the line
GRUB_DEFAULT= 0 to
GRUB_DEFAULT="Windows XP Professional x64 Edition (on /dev/sda2)"

3) give the command :- sudo update-grub & reboot