Correct option is B
The correct substitution of the highlighted segment is “the food is ready.”
Error identification: The phrase "will be ready" is future tense, but the context requires the present tense "is ready" to match the condition being checked.
Grammatical Rule used: When indicating a condition that needs to be checked in the present, the present tense "is ready" is used.
Corrected sentence: Drop me a message when the food is ready.