Final answer:
A preschool boy wearing nail polish is most likely to be shunned by peers due to strict societal gender norms at that age, which makes such an expression of gender non-conformity more socially challenging.
Step-by-step explanation:
Among the preschool options listed, the boy who wears nail polish is most likely to be shunned by age mates. Societal gender norms, especially in preschool-age children, tend to be rigid, and boys are often expected to conform to traditional gender roles. While girls may occasionally cross these boundaries with less scrutiny, such as playing with trucks or wearing boys' shirts, a boy partaking in an activity or style heavily associated with femininity, such as wearing nail polish, may face greater social challenges from peers who are influenced by conventional gender expectations. This reflects a form of gender socialization where societal expectations dictate how children should behave and appear based on their gender.