Answer:
They are physical changes.
Explanation:
This is because there in no chemical reaction taking place, just a physical change.
A physical change in a change in which the chemical structure of the substance does not change. Ice, water and steam are all the same on a molecular level, thus changing from ice to water or from water to steam are physical changes.
A chemical change is a change in which the chemical structure of the substance undergoes a change, since this does not happen going for A to B or B to C they are not chemical changes.
It is B, smoke and air pollution can stress the lungs and cause things like Respiratory distress if not wearing a proper mask. That is why in places with massive amounts of air pollution many people will wear face masks.
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:
.
