Why do I get "No root file system is defined" when I try to install Ubuntu in a partition?

Why am I getting the message "No root file system is defined" when trying to install Ubuntu in a particular partition.

If you are getting the above alert message while installing Ubuntu on a partition, you should follow bellow steps to proceed:

1- Choose the "Ext4 journaling file system" from dropdown.

2- Choose "/" mount point from dropdown. and click ok button.

Now it will start installing Ubuntu on that partition. Please refer the below image for your better understanding.