Final answer:
The answers provided are based on stoichiometry, the concept of moles, and Avogadro's number. The questions involve calculating numbers of atoms, molecules, and mass from chemical equations and molar masses.
Step-by-step explanation:
1) The number of atoms in a 12.0 g sample of carbon is B. 6.02 \u00d7 10^23 atoms. We know this because one mole of carbon (12 g) contains Avogadro's number of atoms (6.022 \u00d7 10^23 atoms).
2) To find out how many grams of potassium iodide will produce 750 grams of silver iodide when there is an excess of silver nitrate, you would use the stoichiometry of the balanced equation. However, without the molar masses of the compounds, the exact answer cannot be provided here.
3) The molecular formula of a compound with an empirical formula of C2H5 and a molecular mass of 116 grams/mole is D. C8H20. The molar mass of the empirical formula (C2H5) is 29 g/mol. By dividing 116 by 29, we get 4, which means the molecular formula has four times the number of atoms as the empirical formula.
4) To find how many grams of boron are needed to completely react with 492 g of oxygen gas, we need to use the molar mass of oxygen and the balanced equation. Without the molar mass of boron, the calculation cannot be completed here.
5) The number of molecules in 4.90 grams of H2SO4 is B. 3.18 \u00d7 10^23 molecules. This is determined by calculating the moles of H2SO4 (using its molar mass from a periodic table) and then multiplying by Avogadro's number.
6) The mass of five moles of helium gas is C. 20 g. This is because one mole of helium gas has a mass of 4 grams, so five moles would have a mass of 5 \u00d7 4 = 20 grams.