Here "describe" is not a verb, its an infinitives - "to describe"

Moreover the subject is not "the work" - the subject is "aperiodic tiles"

The action verb here in this sentence should be plural "are", since "aperiodic tiles" is a plural subject.

But I cannot understand the significance of "comma" in the non undeline portion of the sentence

"The work of mathematician Roger Penrose in the early 1970s, on the geometry "

and "the geometry" -
We can write - "the book" or "the chapter".
But how is "the geometry".

Can anyone please throw some light on these ?

The work of mathematician Roger Penrose in the early 1970s, on the geometry of what are called aperiodic tiles, turned out to describe the architecture of a previously unknown class of crystals.

The bold text "on the geometry of what are called aperiodic tiles" modifies 'work';

The sentence is
The work of mathematician Roger Penrose in the early 1970s (ignore modifier) turned out to describe the architecture of a previously unknown class of crystals.

Verb is 'turned out' --> is a phrasal verb

I think "the Geometry of the Tiles" is fine but not just "the Geometry"

jainrahul1985 wrote:The work of mathematician Roger Penrose in the early 1970s, on the geometry of what are called aperiodic tiles, turned out to describe the architecture of a previously unknown class of crystals.
(A) what are called aperiodic tiles, turned out to describe
(B) what is called aperiodic tiles, describes
(C) aperiodic tiles, describing
(D) so-called aperiodic tiles, describe
(E) aperiodic tiles, it turned out to describe

OA A . how come "describe" agrees with "work"

In B, since what refers to tiles (plural), the verb (is) cannot be singular. Eliminate B.

In C and E, the subject (the work) lacks a verb. Eliminate C and E.

In D, describe does not agree with its subject (the work). Eliminate D.

The only viable answer choice is A, but I'm troubled. The modifier on the geometry is quite far from the noun that it modifies (the work). What is the source of this question?

A few notes:
It is fine to say THE geometry of X. In this context, the geometry of means the shape or relative arrangement of.
In A, the work is the subject of the verb turned out. To describe is the direct object of turned out. An infinitive can serve as the direct object of a verb:

The players expect to win.

Here, to win is the direct object of expect. What do the players expect? They expect TO WIN.