Which desert is home to the world's highest sand dunes?

Which desert spans across several countries in North Africa? Which desert is home to the highest population density? What is the name of the desert that covers parts of Kazakhstan and Uzbekistan? What is the largest desert in the world? In which country is the Karakum Desert located? In which country is the Great Victoria Desert located? Which of the following deserts is the largest in the Middle East? In which continent is the Australian Outback located?