Which of the following statements is true regarding the Ottoman Empire? The Ottoman Empire was named after its founder, Orhan.
The Ottoman Empire existed for about six decades.
The Ottoman Empire was ruled by an emperor.
Many western Europeans perceived the Ottoman Empire to be a threat.

C and D are True.

Explanation:

These are why A and B are incorrect and C is partial:

The Ottoman Empire was formed in 1299 by its founder Osman Gazi, or Osman I. It was not named after Orhan but after Osman. That's why we call it the "Ottoman" empire since Ottoman meant Osman in Ottoman Turkish.The Ottoman Empire did not exist for 6 decades, but for around 6 centuries. They existed from 1299 to 1919 (1919 is Debatable). The Ottoman's Strongest period was during the reign of Suleyman the Magnificent, or Suleyman the Lawgiver.The Ottoman Empire was ruled by a Bey for the first decades of its existence until it upgraded to an Empire and was ruled by a Sultan. After the conquest of the Mamluk Sultanate (Egypt), the Ottomans Captured the holy cities of Mecca and Medina. This allowed for the Ottoman Sultan to be crowned the Caliph (Caliph is not the pope of the Islamic world, but a descendent of Mohammad). While many western powers did see the Ottomans as a threat, they mostly played around with the Empire and its policies. The Ottomans were a huge strength and was considered a European power During the Rule of Yavuz Sultan Selim (Selim I) and expanded farther into Europe during the rule of Suleyman the Magnificent. They lost the title of "European Power" during the 18th century and fully went into decline during this period too. They were conquered and dissolved in 1919.

Hope This helped.

-Greg