Final answer:
Trigonal pyramid shapes are polar when the central atom has one lone pair, creating an asymmetric charge distribution.
Step-by-step explanation:
Trigonal pyramid shapes are polar when the central atom has one lone pair (Option C). The presence of lone pairs affects the molecular geometry. When the central atom has one lone pair, it leads to a trigonal pyramidal molecular shape. This lone pair creates an asymmetric distribution of charge, resulting in a polar molecule. In a trigonal bipyramidal electron-pair geometry, lone pairs preferentially occupy equatorial positions because this minimizes repulsions with other electron groups.