Which of the following scripts of ancient India was mostly written from right to left?

The correct answer is Kharoshti.

Step-by-Step Explanation:

1. Understanding Ancient Indian Scripts:
Ancient India had several major writing systems, among which Brahmi and Kharoshti were the most prominent during the ancient period.

2. Analyzing the Kharoshti Script:
Kharoshti (also spelled Kharosthi) was an ancient script used primarily in ancient Gandhara (present-day northwestern Pakistan and eastern Afghanistan) to write the Gandhari Prakrit and Sanskrit languages.
Unlike most other Indian scripts derived from Brahmi (which are written from left to right), Kharoshti was mostly written from right to left. It was contemporary to Brahmi and was heavily influenced by the Aramaic alphabet, which accounts for its right-to-left directionality.

3. Evaluating Other Options:
- Brahmi: The ancestor of almost all modern Indian scripts, primarily written from left to right.
- Nandnagari: A northern variant of Nagari script, written left to right.
- Sharada: An ancient script of Kashmir belonging to the Brahmic family, written left to right.

Therefore, Kharoshti is the ancient Indian script that was mostly written from right to left.