Why are the masses of some elements listed as whole numbers in parentheses?

The atoms of a solid aluminum can are close together, vibrating in a rigid structure. if the can is warmed up on a hot plate, what happens to the atoms?

Which is the most concentratic acid

An engineer wishes to design a container that will hold 12.0 mol of ethane at a pressure no greater than 5.00x10*2 kpa and a temperature of 52.0 degrees celsius. what is the minimum volume the container can have?