Correct answer only ! i cannot retake this and i need all correct answers !

true or false: doorbells, scrap yards, and rock concerts are all examples of every day uses of electromagnets.

Could someone me find the answer to this problem.

At very high pressures, gases become and will eventually a) more dense; become hotter b) more dense; change to a liquid or solid c) less dense; combust d) less dense; turn into a liquid

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.