Your mass can never change no matter where you are since mass is the amount of matter you contain. By going to the moon, you do become lighter due to the weaker gravity but the amount of matter that you are made of (your mass) does not change.
I hope the helps. Let me know if anything is unclear.
Because the powder has more finer and larger surface area hence it absorbed faster and it becomes more effective in performance compared to the tablet that will still need to be dissolved before it is been assimilated into the body system.
