Explanation:

- Option 1: Harappan

- The Harappan script is associated with the Indus Valley Civilization.

- It's undeciphered and not directly related to modern scripts.

- Limited knowledge makes it hard to trace a lineage to modern scripts.

- Option 2: Brahmi

- It is widely regarded as the mother of modern Indian scripts.

- Developed during the Mauryan Empire in 3rd century BCE.

- Various modern scripts like Devanagari stem from Brahmi.

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- Option 3: Devanagari

- It's a descendant of the Brahmi script.

- Used for Sanskrit, Hindi, and other languages, but not the origin.

- Option 4: Bengali-Assamese

- This script evolved from Brahmi.

- Used primarily for writing Bengali and Assamese languages.

Brahmi is indeed the mother of all modern Indian scripts.