[ Grammar ] How to use the word " effective " ?
We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager,______ next Monday.

(A) effect (B) effected (C) effectiveness (D) effective (E) efficient

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M-W Learner's Dictionary

http://www.learnersdictionary.com/definition/effective

3 : starting at a particular time — used to introduce a clause
Effective [=starting, as of] tomorrow, the store will be open until 8:00 p.m. every day. 
Effective next month, the landfill will no longer accept old televisions. 

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Question:

Q1: Can we explain the sentence as 『 We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager, ( which is / which will be ) effective next Monday. 』

and the antecedent of “ which ” is “ We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager ” ?

or Is it just an idiomatic expression ?

Q2: “ Effective tomorrow / next month,………. ” is a common expression in daily life ?

Thanks

Question

[ Grammar ]  How to use the word " effective " ?
We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager,______ next Monday.

(A) effect  (B) effected  (C) effectiveness  (D) effective  (E) efficient

———

M-W Learner's Dictionary

http://www.learnersdictionary.com/definition/effective

3  : starting at a particular time — used to introduce a clause
Effective [=starting, as of] tomorrow, the store will be open until 8:00 p.m. every day. 
Effective next month, the landfill will no longer accept old televisions.

———

Question:

Q1: Can we explain the sentence as 『   We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager,  ( which is / which will be ) effective next Monday.   』

and the antecedent of “ which ” is “  We regret to announce that Mr. Charles Appiah has resigned his position as senior sales manager   ”  ?

or    Is it just an idiomatic expression ?

Q2:  “  Effective tomorrow / next month,………. ”   is a common expression in daily life ?

Thanks

Answer

The term, "effective" or "effective immediately", does tend to be a business term because it is more formal. 
In everyday conversation, people would say, "I heard that the new requirements COME INTO EFFECT next month".
Or
"STARTING next month, you will need a parking permit to leave your car overnight on the street."

Hope this helps

Answer

I can answer #2.  We use the expression a lot at work, not at home.