Official Solution:
Zirconium Nickel alloy is sold in not only various forms, such as bar, ingot, ribbon and foils, but it is also available in various grades, such as Reagent and technical grade and Agricultural and Pharmaceutical grade.
A. Zirconium Nickel alloy is sold in not only various forms, such as bar, ingot, ribbon and foils, but it is also
B. Zirconium Nickel alloy is not only sold in various forms, such as bar, ingot, ribbon and foils, it is also, as well
C. Zirconium Nickel alloy not only is sold in various forms, such as bar, ingot, ribbon and foils, but also
D. Not only Zirconium Nickel alloy is sold in various forms, such as bar, ingot, ribbon and foils, but also
E. Zirconium Nickel alloy is not only sold in various forms, such as bar, ingot, ribbon and foils, but also
A. Parallelism is not maintained in the construction “not only A…. but also B”. Here A = (various) forms, a noun, whereas B = it is (available), a clause.
B. The construction “not only…also, as well…” is grammatically wrong.
C. Parallelism is not maintained in the construction “not only A, but also B”. Here A = is (sold), a verb, whereas B = available, an adjective.
D. Parallelism is not maintained in the construction “not only A, but also B”. Here A = Zirconium Nickel alloy is sold, a clause, whereas B = available, an adjective.
E. Correct. Parallelism is correctly maintained in the construction “not only A, but also B”. Here A = sold, an adjective, and B = available, also an adjective. Question may arise that “is sold” is a compound verb, but for a compound verb as this one, the second part is equivalent to an adjective. For example The house is sold = sold house, A room is available = available room.
Answer: E