Answer : 4. "75"
Explanation :

1. According to Section 2 of the Antiquities and Art Treasures Act, 1972, 'antiquities' include 'any manuscript, inscription or another document which is scientific, historical, literary or aesthetic and which is in existence for not less than 75 years '

2. Thus, any artefact that has been in existence for at least 75 years is considered an antiquity in India.

3. Antiquities are considered an important part of the cultural heritage of India and there are legal provisions for their protection.