A successful ascent of Mt. Everest is rendered tremendously difficult

EducationAisle
I think in the question a bunch of people seem to miss the point. Can you let me know if my understanding is okay?
A successful ascent of Mt. Everest is rendered tremendously difficult by numerous obstacles, not the least of which is the challenge of adjusting to the decreased atmospheric pressure and correspondingly low oxygen availability that characterize very high altitudes.

Lets first consider this sentence
The new models explained alot of sub-atomic particles, some of which were recently discovered
Whats the subject of were? subatomic particles! Since some take the singular/plural property of what follows and which here refers to sub-atomic particles.

Coming back to our sentence
difficult by numerous obstacles, [i]not the least of which is the challenge of adjusting ...
what does which refer to? Numerous obstacles. The sentence structure is not inverted or anything. The reason why this is singular is because of the word not the least . Just like One of the oranges is singular. not the least of numerous obstacles is also singular, and hence the requirement for singular verb.

DanTe02, Eg- Now that he has a cushy job, money and success are the least of his troubles. I don't think the use of least makes the subject singular. What are you thoughts on my example?

Brian123 I think your construction is very different. The construction you're using
Whats the subject in the independent clause. Money and success plural

For your example to match our question. It would be Not the least of X is Y.
I would like to point two things.
1) Money and success are plural and least of his troubles should be one entity, the phrase least of his troubles mean only one among many.
2) After a bunch of googling, I came to the conclusion that the structure is indeed inverted in our question and Not the least of X can be both singular or plural Not the least of troubles = A bunch of troubles - 1. My analogy was adding the word not does not change the singular plural property , a analogy which is perhaps plain b.s now that I think of it.
One of the X is singular. Least of X is singular. Atleast X maybe singular plural, Not One of the X can be singular plural, One X is singular

Also the above is just me babbling, We can have experts to confirm this. GMATNinja Any thoughts on this?

It might not be a good idea to look at "which" in isolation here. "not the least of which" is equivalent to saying "one of the more important of them is".

EducationAisle Yes expert thats my point. Just like One of apples is singular
does the phrase not the least has this similar property?
or is this hypothesis okay

Yes, that's is correct. Though I did notice that this is not an official question.

Would be interesting to see if someone can point us to an official question that uses/tests this phrase.

Doesnt 'that' always modify the noun immediately preceding it?

Option D in the following question is ruled out because using 'that' for compound nouns distorts the meaning


https://gmatclub.com/forum/arteriviruse ... 03699.html

GMATNinja MartyTargetTestPrep

Could you please help me here, there are cases when we use a singular verb for subjects that sounds plural but actually represents a general idea. "Characterize" is apparently the correct verb for the subject "very high altitudes". But how do we understand that "very high altitudes" here is not a general idea but something plural? Could you please share your thoughts and guidance here?

@veritasKarishma can u please help with this question. Isnt "not the least of which" represent the subgroup modifier, and the entity being modified here is the obstacles and hence the corresponding verb should be plural and not singular.