Answer: D, splitting water into hydrogen and oxygen is a chemical change.
Answer:
Considering the half-life of 10,000 years, after 20,000 years we will have a fourth of the remaining amount.
Explanation:
The half-time is the time a radioisotope takes to decay and lose half of its mass. Therefore, we can make the following scheme to know the amount remaining after a period of time:
Time_________________ Amount
t=0_____________________x
t=10,000 years____________x/2
t=20,000 years___________x/4
During the first 10,000 years the radioisotope lost half of its mass. After 10,000 years more (which means 2 half-lives), the remaining amount also lost half of its mass. Therefore, after 20,000 years, the we will have a fourth of the initial amount.
Answer:
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Explanation:
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Molar mass Na = 23g/mol
46g = 456/2 = 2mol
1mol = 6.022*10^23 atoms
2mol = 2*6.022*10623
= 1.204*10^24 atoms