Acids react with calcium carbonate and more specifically carbonate to form carbon dioxide. An acid will give protons to the carbonate anion to produce carbonic acid which then decomposes into carbon dioxide and water. I hope this helps. Let me know if anything is unclear.
Answer:

Explanation:
Although the context is not clear, let's look at the oxidation and reduction processes that will take place in a Fe/Sn system.
The problem states that anode is a bar of thin. Anode is where the process of oxidation takes place. According to the abbreviation 'OILRIG', oxidation is loss, reduction is gain. Since oxidation occurs at anode, this is where loss of electrons takes place. That said, tin loses electrons to become tin cation:

Similarly, iron is cathode. Cathode is where reduction takes place. Reduction is gain of electrons, this means iron cations gain electrons and produce iron metal:

The net equation is then:

However, this is not the case, as this is not a spontaneous reaction, as iron metal is more reactive than tin metal, and this is how the coating takes place. This implies that actually anode is iron and cathode is tin:
Actual anode half-equation:

Actual cathode half-equation:

Actual net reaction:

Adult Bone Marrow has stem cells that are not as "good" as embryonic ones but they still can become red blood and skin cells
Answer:
19.9 atoms
Explanation:
Grams --- Moles --- Atoms
You're converting from atoms (molecules) to moles.
You do not have to calculate the mass of "di phosphorus pentoxide."
Since you're already given 1.2x10^25 atoms, you start with that. You need to cancel out the atoms, so you need Avogadro's number as shown in the image.
(This has nothing to do with the problem) But in case if you're wondering, the "di" in phosphorus means there's 2 phosphorus and the "pent" means that there are 5 oxygens. So P2O5. Go to your periodic table, multiply their respective atomic masses. You would multiply phosphorus twice and oxygen 5 times. And add them up to get the overall mass.
I hope this helped!
Exothermic reactions transfer energy to the surrounding, usually as heat.