Nuclear fusion in the sun involves hydrogen (h) atoms combining to form helium (he). a student claims that since the atmosphere contains hydrogen, any fusion reaction on earth would result in an uncontrolled chain reaction. what is wrong with the student's reasoning?

the hydrogen in air is not densely packed enough for an uncontrolled chain reaction.
uncontrolled chain reactions can only happen during nuclear fission.
it is impossible to cause a fusion reaction to happen anywhere outside of the sun.
we are safe because there is no radioactive hydrogen in the air.