Mid-Chain resolution vs trigger effects

Scenario:

Opponent:
*Face-up Infernity Archfiend
*3 set traps ( Bottomless Traphole , Infernity Break and Infernity Barrier )
*No Hand cards.

My field:
*1 set mask change
*1 Mystical space typhoon

I summoned E.HERO Neptune and my opponent responded with Bottomless traphole. I then chained my set Mask Change targetting my E.HERO Neptune (my opponent did not respond).
When resolving the chain, I summoned M.HERO Acid via Masked Change thus triggering it's effect.

Question: Can my opponent respond by activating Infernity Barrier on M.HERO Acid's effect?

What in the world is E Hero Neptune? A google search did not return me any result.

But anyway I am just gonna assume that it is a Water Attribute E hero monster with no effect since you did not state any.

In this case, the chain is

Chain 1: Bottomless Traphole
Chain 2: Mask Change

Resolving the chain

Mask Change summons Acid (at this point you cannot activate acid effect because bottomless is still on the Chain)
Bottomless resolves

Because Acid effect is mandatory, it is now put on a new chain which your opponent can respond to which in your case is Infernity Barrier.