Ninth day Prayers for Navratri is dedicated to Goddess Siddhidatri. It is chanted on March 28, 2015 during Chaitra Navratri. Navratri Day 9 Mantra in Hindi is given below. There are three mantras. First is Mool Mantra for eighth day of Navaratri. Second is Dhyan Shloka dedicated to Goddess Siddhidatri. Third is a Stotra. You can chant also prayers like Lalita Sahasranama on the day.
There is no need to chant all mantras. Most devotees chant just the mool mantra.