Which of the following statements best describes the relationship between elements and compound

What is the number of moles of chemical units represented by 9.03x10^24? and how do i show work? (dumb it down )

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 ?

Which symbol can be used to indicate the pressure at which a chemical reaction is carried out? 25°c 2 atm pa