@Brian_BH Constitutional isomers share the same molecular formula. Other aspects like connectivity & physical properties are different; I noticed that the changed tags do not include 404181. Please clarify if this tag should be included & share the rationales for the other tags
Sorry, misstated. For 404181 it requires known that they share the same formula (as one of the discriminator answer options states the opposite). I think I just got my eyes crossed after too much time at the computer. 
QID 403236:
Question asks to define whether two example molecules are structural isomers or not. Requires the explicit understanding that, while they may differ structurally, they have the same chemical formula (necessitating their definition as structural isomers, rather than other discriminator options that would not apply in this case).
QID 401039:
Question gives an example compound and asks to identify which answer options are a structural isomer of the given example. Requires the understanding that it must have the same formula, though can have different connectivities, than the given example. Other answer options all vary in their chemical formula and, thus, would be inappropriate answer options.
QID 402080:
Requires the explicit knowledge that two given isomers are not structural isomers, given that they do share the same chemical formula but cis-trans isomers (and thus have the same relative connectivity). In this case, it requires the explicit knowledge of what constitutes (no pun intended) a constitutional isomer as a negative discriminator to avoid an incorrect answer.
QID 401888:
Example gives two compounds and asks to identify them as -mers of each other (enantiomer, diastereomer, etc.). Requires the explicit understanding that sine the example molecules have the same formula and connectivity, that they cannot be constitutional isomers (which is a negative discriminator that must be eliminated in order to elect the appropriate answer option). Requires the additional understanding of what constitutes (again, no pun intended) a conformational isomer but in order to arrive at the correct answer it must also be discriminated that they do not qualify as constitutional isomers as a potential answer option.