Explain a simple way to calculate the mass of an atom based on Chadwick's discovery. Help would be appreciated:)

Calculate the molarity of 48.0 ml of 6.00 m h2so4 diluted to 0.250 l .

What is the mass of 0.46 mol of mgcl2

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?