Which of the following pairs is not correctly matched

Answer: Option A

Date palm is dioecious, not monoecious. This is not correctly matched. In Date palms, the male and female flowers develop on separate individuals.
Papaya is polygamous, with three primary sex types: female, male and bisexual. There are some cases where plants produce more than one kind of flower at the same time.
Walnut trees are monoecious, meaning a single tree contains both male (catkin) and female (pistillate) flowers, allowing the trees to self-pollinate.
Pistachio nut Plants are dioecious, with separate male and female trees. The flowers are apetalous and unisexual and borne in panicles.