Can E.N.D slay Acnologia? If E.N.D is the strongest Demon in the Books of Zeref and if Acnologia can slay countless dragons, is it possible for E.N.D to slay Acnologia?

I mean, when you think about it, Natsu's dad couldn't slay E.N.D, so is it possible for the Demon to slay a dragon like Acnologia?
I highly doubt it.

First of all, we have no evidence to suggest that any slayer magic is of a higher tier than any other slayer magic. Wendy and Chelia were about equal when they fought, and Natsu actually defeated Zancrow in combat despite Zancrow's God Slayer magic. Therefore END's Demon Slayer magic isn't necessarily better than Natsu's Dragon Slayer magic.

Secondly, Natsu is END. That means that we don't have any evidence to suggest that END is anything more than Natsu wielding Fire Demon Slayer magic as effectively as he wields Fire Dragon Slayer magic.

So looking at the matchup, I would argue that Natsu is actually better suited to 1v1ing Acnologia as a Fire Dragon Slayer than as a Demon Dragon Slayer. You see, slayer magic is designed to defeat the entity they are named after. That means Fire Dragon Slayer magic is more effective against dragons than Fire Demon Slayer magic. (Chapter 301, Zealconis states that humans were given the magic to slay dragons. That's logically Dragon Slayer magic, and you can deduce that X Slayer magic means magic to slay X). 

The reason Zeref designed END is because he wanted to get hit with the most powerful Demon Slayer Magic that existed, since Demon Slayer magic is more effective against his demon body. 

At any rate, if Natsu with his super-effective-against-dragons magic can't beat Acnologia without the power of friendship, I doubt he could do so with less effecive magic.