Explain reasons why
helium is used to fill balloon instead of hydrogen having a lighter weight

This flow chart shows the amount of energy that is emitted by each type of light. ultraviolet > blue light > yellow light > red light (maximum energy) (minimum energy) in an experiment, shining which type of light on a strip of metal would be least likely to produce the photoelectric effect? ultraviolet light dim blue light bright red light bright yellow light

Ineed to find the answer of this question because i dont understand it

All motion is caused by force? true or false