Asking about the date on which something happens using "effective"

Hmm, I'd say #2 - #5 are all good and valid, while #1 is rarely used. If you say "take effect from" people would normally expect you to say "through" and give an end date. But for reasons that I don't think have anything to do with grammar, just convention, "be effective from" without an end date is common.

"... be effective on ..." is ambiguous. It could mean only that one day, or it could mean from that day until the indefinite future. People would probably guess from the context. Like if you said, "The new safety regulations will be effective on March 1", people would assume you meant from that day forward. But if you said, "The sale price will be effective on March 1", they'd probably think you meant just for that one day. "... be effective from ..." always means to the indefinite future.

Others have said that "be effective" can also mean "adequate to the purpose". True, but that would be an unlikely meaning when given with a date. If you said, "The new safety regulations will be effective", that would mean that they will, in fact, improve safety. But "The new safety regulations will be effection on March 1" means that's the day they start. I suppose you could imagine a casee where it's truly ambiguous. Like if someone is trying to say that the new safety regulations will be impractical when we install the new machine we're getting on April 1, I suppose he could say, "The new safety regulations will be effection in March", meaning they will be useful in March but will cease to be useful in April. But you could say that sort of thing about all sorts of words and phrases: they could have different meanings in different contexts. Lots of jokes are based on such potential confusion. As well as lots of unnecessary arguments, I suppose.

All are correct, but take effect is preferred to be effective. Take effect on seems most common:

"Changes will take effect on" also has more Google results than the other phrasings.

I think the first four are all correct. I'd tend to use the 'take effect' versions to avoid possible confusion with the sense of 'effective' meaning 'adequate for the purpose'. The final one feels to me to be an informal shorthand - you'd hear it used but it may not be 100% strictly correct.

I would agree that the first 4 are all valid. There is, however, a difference between "effective from" and "effective on" ( and the take effect equivalents ).

If a change is effective "on" a date, a possible implication is that after then, it will not be taking effect - that is, it is a one-off change just for that day. If it is ongoing - which is more likely - then effective "from" is probably better, although the difference is slight.

I would also consider that "take effect" sounds more like some physical or practical change, whereas "effective" implies a change in regulations. So an increase in the number of traffic warders might "take effect from tomorrow", whereas an increase in ther parking charge could be "effective from next week".

However, the differences are very subtle.