I want to install ROS Indigo only, which supports only Ubuntu 14.04, and I have Raspberry Pi 3 kit. Does Raspberry Pi 3 support Ubuntu 14.04?
I'm not sure if it would work but it would definitely be unstable or slow if it worked. There's another version of Ubuntu which works with the Raspberry Pi. It's called Ubuntu MATE, you can download it from here: https://ubuntu-mate.org/download/
There's also a little documentation for Ubuntu MATE on the Raspberry Pi on there: https://ubuntu-mate.org/raspberry-pi/
Ubuntu 14.04 LTS
An Ubuntu 14.04 LTS (Trusty Tahr) image is available for the Raspberry Pi 2, which combines the released 14.04 distribution with a PPA containing kernels and firmware which work on the Raspberry Pi 2.
Warning ! This image, along with the one-off kernel it installs, is no longer maintained. Please use the 16.04 Xenial image instead. Warning !
I would suggest that you go for "ROS Lunar Loggerhead" that supports:
Ubuntu Xenial (16.04)
Ubuntu Yakkety (16.10)
Ubuntu Zesty (17.04)