Fill in the blank with the correct option: Bread and butter ______ good for…

The correct verb to fill in the blank is is. The full sentence is: "Bread and butter is good for health."

Grammatical Explanation: Compound Subjects acting as a Single Unit
In English, the rule of subject-verb agreement generally dictates that compound subjects joined by "and" are plural (e.g., "The bread and the butter are on the table"). However, there is an important exception:

Compound Nouns acting as a Single Unit: When two nouns joined by "and" are so closely linked that they represent a single idea, dish, or concept, they are treated as a singular subject and therefore take a singular verb.

In this sentence, "bread and butter" refers to a single, combined food item/dish, not two distinct items placed side-by-side. Thus, it functions as a singular subject.