Explanation:
Because they share a similar composition, similar chemicals affect their structures in positive or negative ways. For example, fluoride – a staple in many dental practices – strengthens both enamel and eggshells and helps protect them from acids. Acids weaken and break down both substances. Scientists find this particularly concerning given that the ocean is growing increasingly acidic. They fear this may weaken the eggs of some marine species and harm their chance of survival. Most dentists recommend limiting aggressively acidic foods and beverages such as soft drinks.
Given teh equation adn the heat of reaction, reaction 2's heat of reaction can be obtained by simply multiplying teh heat of reaction of 1 by 3. The final answer is -6129 kJ.
Explanation:
Copper(II) sulfide reacts with oxygen gas to give solid copper(II) oxide and sulfur trioxide gas.
The reaction is given as:

When 1 mol copper(II) sulfide react with 2 moles of oxygen gas it gives 1 mol of solid copper(II) oxide and 1 mol of sulfur trioxide gas
The gas formed in above reaction that is sulfur trioxide reacts with water to give sulfuric acid or hydrogen sulfate.
The reaction is given as:

1 mol of sulfur trioxide gas reacts with 1 mol of liquid water to produce 1 molo of liquid hydrogen sulfate or sulfuric acid
Answer:
D) He did not multiply the chlorine and oxygen atoms by the coefficient 4.
Explanation:
The coefficient 4 at the beginning of the chemical formula indicates that there are four Ca(ClO3)2 molecules. Think of this as Ca(ClO3)2 × 4. This means that he had to multiply the number of atoms for each element by 4 as well, so he should've ended up with 4 total calcium atoms (which is correct), 8 total chlorine atoms, and and 24 total oxygen atoms. He did not get all these answers because he didn't multiply the chlorine and oxygen atoms by the coefficient 4.
HM, I think the answer would be D. This is just a guess, so please use it if ou want to answer D it's ok :D