This isn't a good question but I guess!
I will help you with answering this question.
2) mg donates two protons to O.
1 mole = 6.022×10^23 atoms. 1 water molecule = 2 Hydrogen atoms + 1 oxygen atom. So, 1 mole H2O = 1.2044×10^24 hydrogen atoms. Therefore 2 mole H2O will have 2.4088×10^24 hydrogen atoms.
125 Each half life it divides by 2 the amount
1000/2=500
500/2=250
250/2=125