Answer: B) Situational irony.
Step-by-step explanation: An irony is an expression that usually signify the opposite, it is used to give a humorous or emphatic effect. A situational irony is when what happens is contrary, or simply different to what the audience or the characters expect. In the given scenario, we can see a clear example of a situational irony, when little Johnny plants tomato seeds, him and the readers are expecting a tomato plant to grow, but instead an African Violet blooms.