Choose the most efficient and accurate way to prepare a sample containing 0.75 moles of iron (fe) atoms. group the iron atoms in bundles of 1000 atoms so they can be counted faster. take a bar of iron that contains one mole of atoms, measure the length carefully, and remove 1/4 of the bar's length. weigh 41.89 grams of iron. count 4.5 ✕ 1023 fe atoms.

weigh 41.89 grams of iron.

Justification:

Since atoms are not visible (due to its tiny size) there is no way how you can count a specific amount of them. Furthermore, it is not feasible to cut an exact portion of a bar to get an exact number of atoms. That means that it is impossible to perform these tasks: group the iron atoms in bundles of 1000 atoms so they can be counted faster, take a bar of iron that contains one mole of atoms, measure the length carefully, and remove 1/4 of the bar's length, or count 4.5 ✕ 1023 fe atoms.

Scientists (chemists) have established with high precision the atomic masses of the 118 known elements.

The atomic mass is the mass in grams of one mole of atoms of the element.

For iron (Fe), you can find in any periodic table its atomic mass. It is 55.85 g/mol.

Therefor,e you can calculate the mass in 0.75 mol of iron (Fe).

The calculation is done with the equation:

mass in grams = number of moles × atomic mass

mass of Fe = 0.75 moles × 55.85 g/mol = 41.8875 g ≈ 44.48 g (you have to use two significan figures).

Therefore, you can use an analytical balance (a very precise scale found in most chemical laboratories) to weigh the 41.89 g, with high precision and accuracy, and be certain that, if the iron is pure, you will have 0.75 moles.

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current