Does くだく mean “destroy”? What does いい mean at the beginning of a line?

Question

Would the following be a good translation of the text in the above two speech bubbles?

"Everything in this universe is composed of atoms. Destroying something is equivalent to destroying the atoms that compose it"

Also, I'm especially interested in knowing if the Japanese text is implying that atoms are completely destroyed/annihilated or if the atoms are separated or pulverized (but not literally/completely destroyed). I'm having troubles on my own... =/

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Here is a transcription of the two speech bubbles, in case you can't see the images:

「この
　大宇宙にあるもの
　すべてが
　原子でできている
　のよ」

「いい　破壊する
　ということの
　根本は　原子を
　くだく
　ということなの」

Answer 1

The translation of the first sentence sounds fine.

For the second one, "destroy" may be too general for 「くだく」 and "be equivalent to" sounds a little bit different to 「…の根本｛こんぽん｝は」. My suggestion is something like "The essence of destroying something is shattering the atoms that compose it." (I'm not a native English speaker, the wording may be awkward...)

Since it's literally saying "shattering the atoms", i.e.「原子｛げんし｝をくだく」, not "shattering something into atoms", 「原子｛げんし｝にくだく」as in 「粉々｛こなごな｝にくだく」 and 「微塵｛みじん｝にくだく」　may be more appropriate for the "atoms are separated" reading.

As to the 「いい」 that 非回答者 has pointed out, I guess it's something like "understand?" or "all right?" used when a teacher is explaining something to his/her student(s) or in other similar circumstances.