A teacher in her letter to the Principal of her school shall address her as :

Correct option is B

“Madam” is the most formal, appropriate and concise way to address a Principal in official correspondence. It is respectful without being overtly familiar (“My dear madam” is too personal) or dated (“Respected madam” is more common in Indian English but less standard globally). "Madam" conveys the right professional tone, clear hierarchy, and customary formality.
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Information Booster

Letter-writing is a fundamental communication skill in educational administration and the “salutation” sets the tone.

Modern conventions, especially in English-medium schools, prefer direct and dignified terms such as “Sir” or “Madam.”

Such usage is modeled in official school templates and CBSE/ICSE/State board language learning materials, aligning with global standards in business English.

Additional Knowledge

(1) “My dear madam” is overly personal.

(3) “Respected madam” is widely used in India but is less standard in formal Western English.

(4) “Dear madam” is moderately formal but “Madam” is most accepted for official letters to authorities.