The challenge the author of the above passage throws to the public is to achieve

Correct Option: hard work, brotherhood and national unity

The passage emphasizes the continuous "hard work ahead" until the pledge is redeemed. It appeals to the public as "citizens of a great country... equally the children of India with equal rights, privileges and obligations," which underscores national unity and brotherhood. Furthermore, the author warns against communalism and narrow-mindedness in thought or action, which directly advocates for unity and brotherhood. Therefore, the challenge thrown to the public is to achieve hard work, brotherhood, and national unity. Other options like A, B, and C focus on material progress, adventure, or specific political aspects that do not fully capture the moral and nationalistic call for unity and collective labor. Thus, Option D is the correct answer.