Answer:
Approximately 75%.
Explanation:
Look up the relative atomic mass of Ca on a modern periodic table:
There are one mole of Ca atoms in each mole of CaCO₃ formula unit.
- The mass of one mole of CaCO₃ is the same as the molar mass of this compound:
. - The mass of one mole of Ca atoms is (numerically) the same as the relative atomic mass of this element:
.
Calculate the mass ratio of Ca in a pure sample of CaCO₃:
.
Let the mass of the sample be 100 g. This sample of CaCO₃ contains 30% Ca by mass. In that 100 grams of this sample, there would be 
of Ca atoms. Assuming that the impurity does not contain any Ca. In other words, all these Ca atoms belong to CaCO₃. Apply the ratio 
:
.
In other words, by these assumptions, 100 grams of this sample would contain 75 grams of CaCO₃. The percentage mass of CaCO₃ in this sample would thus be equal to:
.
The answer is Physical Change.
The stable ion the sulfur would form is the sulfide ion,
S
2
−
.
Explanation:
A neutral sulfur atom contains 16 electrons. We can know this because its atomic number is 16, which means there are 16 protons in the nucleus. Since the negative charge of the electrons cancels the charge of the protons, the sulfur atom is neutral. The electron configuration of sulfur is
1s
2
2s
2
2p
6
3s
2
3p
4
. The valence shell (the 3s and 3p sublevels) contains six electrons, but it needs eight to become stable. Think of the octet rule. Therefore a sulfur atom will gain two electrons to form the sulfide anion with a charge of
2
−
, with the symbol
S
2
−
.hope this helps
Answer: D
Explanation:
Chlorine is in group 7 or (VII) in Roman numerals, which means it has 7 balance electrons. It only needs one electron to become stable, hence it is next to the noble gases
Aristotle, there was four elements (earth, water, air and fire)
