To solve this problem, we need to identify which plants have zygomorphic flowers. Zygomorphic flowers are those that can be divided into two equal halves in only one plane. Let's analyze each option:$\newline \bullet$(a) Mustard: Mustard flowers are actinomorphic, meaning they can be divided into two equal halves in multiple planes.$\newline \bullet$(b) Gulmohar: Gulmohar flowers are zygomorphic, as they can be divided into two equal halves in only one plane.$\newline \bullet$(c) Cassia: Cassia flowers are also zygomorphic, as they can be divided into two equal halves in only one plane.$\newline \bullet$(d) Datura: Datura flowers are actinomorphic, meaning they can be divided into two equal halves in multiple planes.$\newline \bullet$(e) Chilly: Chilly flowers are actinomorphic, meaning they can be divided into two equal halves in multiple planes.$\newline$Based on this analysis, the flowers that are zygomorphic are Gulmohar and Cassia.$\newline$Therefore, the correct answer is Option 2: (b), (c) Only.