Large scale mining of metal and coal in the region has led to both acid rock drainage, acid water flowing out from abandoned mines, and the deposition of tailings, elements or compounds uncovered during mining, altering the receiving environment to its detriment, but are harmless if collected and disposed of in time. 



(A) acid water flowing out from abandoned mines, and the deposition of tailings, elements or compounds uncovered during mining, altering 


(B) which is the outflow of acidic water from abandoned mines, as well as the deposition of tailings, elements or compounds uncovered during mining, altering 


(C) the outflow of acidic water from abandoned mines, the deposition of tailings, elements or compounds uncovered during mining, which may alter 


(D) acid water flowing out from abandoned mines, the deposition of tailings, elements or compounds uncovered during mining, which may alter 


(E) which is the outflow of acidic water from abandoned mines, and the deposition of tailings, elements or compounds uncovered during mining, which may alter



Doubt- In this question, under option E(correct option), “which may alter” is intended to modify “tailings”, but there is an appositive (elements or compound uncovered during mining) in between “tailing” and “which”.



In that case “which” should refer to nearest noun Mining in appositive, as placement of a “which” modifier should be next to the noun which it modifies, but it doesn’t make sense for “which” to modify Mining as per meaning of sentence.

Can “which” modify a noun slightly far-off from it and can we have an appositive between noun and (that/which) clause?



As with most rules, the ‘which’ rule also has an exception. Remember that ‘which’ can be unambiguous when there is a clear difference in the two nouns within the prepositional phrase. This concept is also applicable to other relative pronouns such as ‘that’, ‘who’, ‘whose’, and ‘whom’.

Examples:

ï The box of toffees, which was on the table, was expensive. P 

In the above example, the verb ‘was’ following ‘which’ clearly indicates the noun that is being modified, i.e., ‘box’. There is a clear difference between the two nouns in the prepositional phrase ‘box of toffees’. 

ï The box of toffees, which were delicious, is expensive. P 

In the above example, the verb ‘were’ following ‘which’ clearly indicates the noun that is being modified, i.e., ‘toffees’. There is a clear difference between the 2 nouns in the prepositional phrase ‘box of toffees’. 

In the given question, like you pointed out, “which” cannot refer to “mining”. 

“which” refers to "tailings", elements or compounds......" 

The plural verb in the non-underlined part- "but are harmless if collected and disposed of in time" is the clue for that.