sudo mount /dev/sda7 /mnt 
sudo mount --bind /dev /mnt/dev 
sudo mount --bind /dev/pts /mnt/dev/pts 
sudo mount --bind /proc /mnt/proc 
sudo mount --bind /sys /mnt/sys 
sudo chroot /mnt /bin/bash
Then I executed-:

root@ubuntu:/# grub-install --root-directory=/mnt /dev/sda1
Unrecognized option `/dev/sda1'
Usage: grub-install [OPTION]
Install GRUB on your EFI partition.

  -h, --help              print this message and exit
  -v, --version           print the version information and exit
  --modules=MODULES       pre-load specified modules MODULES
  --root-directory=DIR    install GRUB images under the directory DIR
                          instead of the root directory
  --grub-mkimage=FILE     use FILE as grub-mkimage
  --grub-mkdevicemap=FILE use FILE as grub-mkdevicemap
  --grub-probe=FILE       use FILE as grub-probe
  --no-floppy             do not probe any floppy drive
  --recheck               probe a device map even if it already exists

grub-install copies GRUB images into the DIR/boot directory specified by
--root-directory.

Report bugs to <bug-grub@gnu.org>.

grub-install --root-directory=/mnt

/mnt/boot/grub doesn't look like an EFI partition.