Two valence states of uranium, one with a deficit of four electrons and the other one with a deficit of six, occurs in nature and contributes to the diversity of uranium’s behavior.

the parallel elements are "one with a" and "the other with a"
we don't need to add "one" after "the other"

(A) the other one with a deficit of six, occurs in nature and contributes
the Subject two valence states is plural therefore cannot take the singular verbs "occurs" and "contributes"

(B) the other one a deficit of six, occur in nature and contribute
this option also has a meaning error... the other valence state itself is not a deficit of six.. therefore this option is wrong.

(C) the other with a deficit of six, occurs in nature and contributes
the singular verb "occurs" illogically refers to the plural subject "two valence states"

(D) the other with a deficit of six, occur in nature and contribute
D is the correct option

(E) one with six, occurs in nature and contributes
one here generalises whereas we are specifically talking about the other valence state of uranium. therefore this option is wrong
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