What is lighter than air but can be never lifted?

Do stars get bigger or smaller as they age? What are the condition for an object to stay at rest to keep moving at constant velocity? What is a dormant bacteria called? What does the word unusual means? Is the date on the eastern side of the date line one day ahead or one day behind the date on the western side of the line? 3.4 miles is how much of a kilometer? How much water to add to plaster? What is 82 square kilometers in meters? Do people live in the great rift valley? What tissue can move itself? Who is Aunty Acid? Why are chemists interested in theoretical and actual yields? What is the oldest piece of space debris still in orbit? Is wind-chill temperature greater than air temperature? What is likely to be the oldest molecule and is thus considered a molecular fossil? What is the Biggest measurement ever? What is a circle inside a circle called? What do you need to know if you have two compounds of iron and chlorine to know they are the same compound? What is used to represent a specific amino acid? What time is it in Adelaide when its 11pm in London?