Which substance on Table H has the weakest intermolecular attractions at 75 degrees celsius?

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

fe 55.85 g/mol and h2o 18.02 g/mol.

the answer your looking for is c).

yes the answer is total mass in unchanged   : )