Select the most appropriate option that rectifies the error(s) in the following sentence.
One must do his/her duty proparly.

The correct option that rectifies the error(s) in the sentence is One must do one's duty properly.

Step-by-step breakdown of the errors and corrections:

1. Pronoun Agreement:
When the indefinite pronoun "One" is used as the subject of a sentence, it must be followed by its possessive form "one's" throughout the sentence, rather than "his/her" or "his". Therefore, "his/her" should be replaced with "one's".

2. Spelling Error:
The word "proparly" is misspelled in the original sentence. The correct spelling is "properly".

Combining these corrections gives the grammatically correct sentence:
"One must do one's duty properly."