10 most difficult Saudi Arabia riddles

The Arabian Desert is twice as large as the Gobi, and four times larger than Great Victoria and Kalahari. It occupies most of the Arabian Peninsula.

The Rub' al Khali desert is the largest continuous sand desert in the world, encompassing most of the southern third of the Arabian Peninsula. The desert covers some 650,000 km² (250,000 sq mi) including parts of Saudi Arabia, Oman, the United Arab Emirates, and Yemen.

Sweet crude oil contains small amounts of hydrogen sulfide (in contrast to sour crude oil). Low-sulfur crude oil is in high demand as it is used to produce high-quality gasoline without the need for expensive processes of removing sulfur impurities. The term "sweet" originates from the fact that a low level of sulfur provides the oil with a mildly sweet taste and pleasant smell. Nineteenth century prospectors would taste and smell small quantities of oil to determine its quality.

Mecca was long ruled by Muhammad's descendants, the sharifs, either as independent rulers or as vassals to larger empires. It was absorbed into Saudi Arabia in 1925.

During the Hajj, about 6 million pilgrims gather to circle the building on the same day.

The shahada is the Muslim declaration of belief in the oneness of God and acceptance of Muhammad as God’s prophet. The declaration in its shortest form reads: There is no god but God, Muhammad is the messenger of God.

According to Muslim beliefs, the Quran was revealed to Muhammad by the archangel Jibril (Gabriel). Muhammad was illiterate, so the "canonical" version was written by Zajd ibn Sabit, his personal secretary.

From the 1940s, the city entered the long period of modernization and planned development under king Saud. Today, Riyadh resembles American metropolies with its grid layout pattern and neighbourhoods connected by high-performance main roads to the inner areas.

The Red Sea is the world's northernmost tropical sea with coral reefs. The name of the sea may come from the seasonal blooms of the red-coloured cyanobacterias Trichodesmium erythraeum.

In its modern period, Mecca has seen tremendous expansion in size and infrastructure. Mecca has become one of the most cosmopolitan and diverse cities in the Muslim world, although non-Muslims are prohibited from entering the city.