Question

A drug is developed that, due to its molecular shape, blocks the action of substance

a. which shape would the drug molecule most likely resemble?

Answer 1

It should have the shape number 2.

The substance A has a region that will bind to the nerve cell Y.
The drug developed that's going to block the substance A, will have to have a region that is complementary to the substance A. If those two regions get linked the substance A will have nowhere else to bind.