Which of the following describes an element? Matter made up of only one type of atom
A substance made of two or more types of atoms
Two or more types of atoms chemically bonded together
Two or more types of atoms that are not chemically bonded

Could someone . i have tried to solve myself but my calculation is off

Describe uniform velocity and variable velocity in short

An insulated 40 ft^3 rigid tank contains air at 50 psia and 120°f. a valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. the air temperature during this process is kept constant by an electric resistance heater placed in the tank. determine the electrical work done during this process.