**Explanation:**

The Mughal emperor who adopted the title of Alamgir was Aurangzeb.

**Explanation in detail:**

1. The Mughal Empire was one of the largest and most powerful empires in the Indian subcontinent. It was founded by Babur in 1526 and lasted until the mid-19th century.
2. The Mughal emperors were known for their grandeur, wealth, and cultural contributions to the region. They adopted various titles to signify their power and authority.
3. Aurangzeb was the sixth emperor of the Mughal Empire, ruling from 1658 until his death in 1707. He was the son of Shah Jahan, the builder of the famous Taj Mahal.
4. Aurangzeb adopted the title of Alamgir, which means "World Seizer" or "Conqueror of the World." This title reflected his ambition and desire to expand the Mughal Empire to its greatest extent.
5. Aurangzeb was known for his strict adherence to Islamic law and his efforts to impose Islamic practices on the empire. He banned many Hindu festivals and temples and implemented policies that were detrimental to non-Muslims.
6. Despite his military successes and the expansion of the empire under his reign, Aurangzeb's strict religious policies and heavy taxation led to widespread discontent among his subjects.
7. The Mughal Empire began to decline after Aurangzeb's death, as his successors were unable to maintain the empire's vast territories and faced challenges from regional powers and European colonial powers.
8. The adoption of the title Alamgir by Aurangzeb is significant because it reflects his ambitions and the religious policies he implemented during his reign. It also marks a turning point in the history of the Mughal Empire, as his strict rule and the decline of the empire began during his reign.

Hence, the correct answer is option C) Aurangzeb.