Answer:
millions of years sometimes even hundred of millions of years
You would have to dig up 261 g of sylvanite.
Mass of sylvanite = 73.0 g Au × (100 g sylvanite/28.0 g Au) = <em>261 g</em> sylvanite.
Answer:
Astatine is a halogen with several isotopes that all have short half-lives.
Which of the following combinations of mass number and neutrons are possible as isotopes of astatine? Choose one or more:
i) A = 211, n = 127
ii) A = 210, n = 125
iii) A = 220, n = 134
iv) A = 207, n = 122
v) A = 209, n = 124
Explanation:
The mass number is the sum of the number of protons and the number of neutrons in an atom.
Atomic number of At(astatine ) =85
That means it has --- 85protons.
Its mass number A=210
Hence, the number of neutrons in At are:

Second option:
ii) A=210 , n=125 is the answer.
Answer:
A. Group 4
Explanation:
Also called carbon family or the tetrels
Answer:
It is important because it separates the area that the process is happening from its surroundings, and it's easy to measure and make observations by doing that.
Explanation:
The system is the part of the universe that is separated for study. It has a frontier, which is the limitation of it, and the external area is the surroundings.
In the system the chemical and physical process is happening: reactions are taking place, gas is expanding, heat is being absorbed or lost, etc.
So, to understand the process that is happening, it's necessary to define the system under study because the measurements, analyze, and observation will be easily done.