Which day of the week fell on 6 October 1980?

Correct answer: Option B — Monday. Counting total odd days up to this date, or using a verified Gregorian calendar calculation, gives weekday index 0 where Monday is 0; therefore the day is Monday. Option A (Tuesday) is rejected because it does not equal the computed result; it represents a counting, direction, leap-year, interval, or hand-motion error. Option C (Wednesday) is rejected because it does not equal the computed result; it represents a counting, direction, leap-year, interval, or hand-motion error. Option D (Friday) is rejected because it does not equal the computed result; it represents a counting, direction, leap-year, interval, or hand-motion error.