Hydrogen is a pure substance represented by the chemical symbol h. which of the following best describes hydrogen
a. hydrogen is a compound made of only one kind of atom.
b. hydrogen is a compound made of two or more kinds of atoms.
c. hydrogen is an element made of two or more kinds of atoms.
d. hydrogen is an element made of only one kind of atom.

Americium-241 undergoes fission to produce three neutrons per fission event. if a neutron-absorbing material is mixed in with this sample so that the rate of neutron production drops down to 1.8 neutrons per fission event, which will be effective at achieving a critical mass? check all that apply. remove a deflective shield surrounding the sample. remove absorbent material mixed in with the sample. compress the sample of americium-241.