In substitution type of questions, some particular objects are assigned code names. Then a question is asked that is to be answered in the code language.
If banana is apple, apple is grapes, grapes is mango, mango is nuts, nuts is guava, which of the following is a yellow fruit ?
Clearly, 'mango' is the yellow fruit but 'mango' is called 'nuts'.
So, 'nuts' is the yellow fruit.