The image attached at the bottom hold the 2 questions that need to be answered. I would really appreciate it if some one could answer them for me. :) i will mark brainliest answer aswell!!

Find the mass in grams of 1.37x1020 particles of h3po4

What is a metal replacement reaction

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.