Nitrolim is a chemical fertilizer, and its composition is the combination of calcium carbide and nitrogen. Calcium carbide is a compound made up of calcium and carbon. Nitrogen, on the other hand, is a chemical element. Therefore, option 2, which states that the composition of Nitrolim is calcium carbide and nitrogen, is the correct answer.

Option 1, which suggests that the composition is nitrogen and limestone, is incorrect. Limestone, also known as calcium carbonate, is a different compound than calcium carbide.

Option 3, which proposes that the composition is calcium carbide and carbon, is not accurate. While calcium carbide does contain carbon, the composition of Nitrolim includes nitrogen, not carbon.

Option 4 states that none of the given options are correct. However, this is not the case, as option 2 accurately describes the composition of Nitrolim.

Therefore, the answer provided in the question is generally correct, and there is no need for an alert regarding its accuracy.