(A) osmium, due to a pattern of density among the elements, holds this distinction, and they call it Unclear weather osmium is called “Lathanide contraction”., or if a pattern of density among the elements is called “Lathanide contraction"
(B) it is osmium that holds this distinction, because of a pattern of density among the elements known as Correct. It is clear that the pattern is called “Lathanide contraction"
(C) osmium, holding this distinction, because of a pattern of density with the elements known as Incomplete sentence. There is no verb.
(D) osmium, holding this distinction, for a pattern of density in the elements is known as Extremely awkward and wordy. Also says that osmium is known as “Lathanide contraction".
(E) osmium, which holds this distinction, because a pattern of density among the elements is known as osmium...is known as. It should be the pattern that is known as

The answer is B.

While many people believe either lead or gold is the densest naturally occurring element, osmium, due to a pattern of density among the elements, holds this distinction, and they call it “Lathanide contraction.”

The idea of the original sentence is not at all clear. We're looking for a choice that expresses that osmium holds this distinction (as the densest) because of a pattern among the elements called Lathanide contraction.

(B) it is osmium that holds this distinction, because of a pattern of density among the elements known as
(C) osmium, holding this distinction, because of a pattern of density with the elements known as no main verb and with is not the correct preposition
(D) osmium, holding this distinction, for a pattern of density in the elements is known as for is not the correct preposition, nor is "in," and says that osmium rather than the pattern is known as Lathanide contraction
(E) osmium, which holds this distinction, because a pattern of density among the elements is known as also says that osmium is known as Lathanide contraction

(A) osmium, due to a pattern of density among the elements, holds this distinction, and they call it
(B) it is osmium that holds this distinction, because of a pattern of density among the elements known as
(C) osmium, holding this distinction, because of a pattern of density with the elements known as - should have a full verb instead of holding
(D) osmium, holding this distinction, for a pattern of density in the elements is known as - same as C
(E) osmium, which holds this distinction, because a pattern of density among the elements is known as - The whole part after WHICH is awkward. Osmium should follow a full verb.

Cheers.
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Official Explanation:

Choice (A) illogically suggests that osmium itself, the very existence of the element itself, is "due to a pattern of density among the elements". Furthermore, the final three words of (A) are a disaster --- "they call it" ---- (a) who is "they"? This pronoun has no antecedent in the sentence; (b) the antecedent of "it" is grammatically ambiguous --- it could be osmium, or the pattern, or the distinction. (A) is incorrect.

Choice (B) uses the emphatic construction discussed in this post --- appropriate, because osmium is contrary to many peoples' expectations on this question. The rest is grammatically correct. This is a promising choice.

The section before the underlined section is a subordinate clause beginning with "while", so the independent clause, the main clause of the sentence, must come in the underlined section. Choice (C) has no verb, and thus would create a sentence with no verb. This is the missing verb mistake. (C) is incorrect.

Choice (D) has an odd construction. After the initial subordinate clause, it has a noun + modifier "osmium, holding this distinction", then a conjunction and an independent clause. This has the effect of leaving "osmium" as a free-floating noun in the sentence, not part of any clause. Furthermore, the "for" clause would introduce an explanation, but here, it illogically suggests that what the pattern is called, not the pattern itself, is the explanation of osmium's properties. (D) is incorrect.

Choice (E), like choice (C), has no verb, and thereby creates a sentence with no main verb. Furthermore, the "because" clause suggests illogically that what the pattern is called, not the pattern itself, is the explanation of osmium's properties. (E) is incorrect.

The only possible answer is (B).

Frequently Asked Questions:

FAQ: How can we distinguish between "due to" and "because of" in this question?

A: Great question! The phrase "due to" must modify a simple noun (a person, place, or thing), while the phrase "because of" must modify a verb.

Here's a great Magoosh GMAT blog post discussing the distinction:

The phrase due to is similar to because of, and in colloquial use they are used interchangeably, but there is a subtle difference. The words “because of” are a compound preposition, and the preposition phrase formed can modify the verb and thus be placed in any part of the sentence. The word “due” is an adjective and must modify a noun.
Let's take a look at some examples:

She did well (verb) on the test because of her hard work and diligence.
We use "because of" here because it modifies the verb "did well."

Her success (noun) on the test was due to her hard work and diligence.
The "due to" here modifies the noun "success."

So "due to" modifies a noun, whereas "because of" has to modify a verb.
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