In which year did the ottoman empire reach its peak and then begin to decline?
1830
1774
1600
1550

Let's say 1600. The Ottoman Empire reached the greatest expanse of its territory and power under Suleiman the Magnificent, the Sultan of the Ottoman Empire from 1520 to 1566. He administered an empire of approximately 20 million people, stretching across the Middle East and North Africa and into parts of Europe. In the decades that followed, Russian power began to grow and Ottoman naval supremacy was challenged by Europeans, notably at the Battle of Lepanto in 1571. So by 1600 the strength of the Ottoman Empire was beginning to take a downturn. But the Ottomans continued to operate (with gradually shrinking territorial holdings) until the 20th century.

The Ottoman Empire was one of the largest empires of the history. It lasted for several hundred years. The Ottoman Empire reached its peak during the reign of Suleiman who ruled from 1520 - 1566. The empire began to decline after its defeat in year 1571 in the battle of Lepanto when it lost almost all of its navy. 

Therefore, from the given options, the best possible answer is Option D.
Year 1600