Final answer:
The correct answer is (a): A trigonal-planar molecule has 0 lone pairs, a bent-shaped molecule with a trigonal-planar electron domain has 1 lone pair, and a trigonal-pyramidal molecule has 4 atoms and lone pairs in total.
Step-by-step explanation:
The question pertains to the VSEPR (Valence Shell Electron Pair Repulsion) theory, which helps predict the shape of molecules based on electron-pair repulsions. For a molecule with a trigonal-planar shape, it has 0 lone pair(s). This means that there are three atoms bonded to the central atom with no lone pairs affecting the shape. When a molecule with a bent shape originates from a trigonal-planar electron domain, it has 1 lone pair; the lone pair replaces one of the atoms, causing the shape to bend. Finally, a molecule with a trigonal-pyramidal shape has a total of 4 atom(s) and lone pair(s) around the central atom, typically with three atoms bonded to the central atom and one lone pair.
Therefore, the correct answer to the student's question is: a molecule that has a trigonal-planar shape has 0 lone pair(s), a molecule that has a bent shape and a trigonal-planar electron domain shape has 1 lone pair(s), and a molecule that has a trigonal-pyramidal shape has 4 atom(s) and lone pair(s) around the central atom. The correct choice is answer (a).