(A) A contribution to a favorite charity being sent insteadWhen read literally, it seems like the charity is being sent instead of flowers, which is not the intended meaning.
Ambiguous and Incorrect.
(B) A contribution being sent to a favorite charity as opposedas opposed of flowers is incorrect, rather the correct phrase is
as opposed to.
Incorrect.(C) To send a contribution for a favorite charity insteadUnambiguously reads that sending a contribution (for a charity) instead of sending flowers is becoming the norm.
Correct.(D) Sending a contribution to a favorite charity insteadSending a contribution to a favorite charity instead of flowers is ambiguous. It may seem like flowers were sent to a favorite charity, whereas the intended meaning is that flowers used to be sent to colleagues.
Incorrect.(E) Sending a contribution to a favorite charity as opposedSame as B. as opposed of is not the correct way to use the phrase.
Incorrect.