Often visible as smog, ozone is formed in the atmosphere from hydrocar

Hello Sheersh,

I know this is a very old post. Yet I am answering it so that if any one else has the same doubt, can find an answer here.

It is true that generally when is used to present the time of an event. However, in certain sentences, when is used to present condition also.

When A happens, B happens. --> The intended meaning is that A has to happen for B to to take place.

This is the usage of when that we see in this official sentence.

The sentence says that when hydrocarbons and nitrogen oxides react with sunlight, then ozone is formed.

Hope this helps.
Thanks.
Shraddha

for simplification modifier part 'two major pollutants emitted by automobiles' can be removed and then we can look at the answer choices which give us complete meaning.
(a)reacts with sunlight has no bearing on the rest of the sentence.(what reacts?)
(b)Often visible as smog,ozone is formed in the atmosphere when hydrocarbons and
nitrogen oxides, two major pollutants emitted by automobiles, react with sunlight.
gives the proper meaning as how the ozone is formed.
(c)ozone is formed in the atmosphere, and when
and is unnecessary here.
(d)ozone, formed in the atmosphere when - looks incomplete, looks as if the sentence tends to convey something after the forming of ozone, but thts not the case here.
(e)same as above.

Let’s understand the main parts in this sentence:

Often visible as smog, ozone is formed in the atmosphere from hydrocarbons and nitrogen oxides, two major pollutants emitted by automobiles, react with sunlight.

So when the essential parts are retained we see that the sentence is setting up a condition – it is saying that ozone is formed when two things react with sunlight.

Now we can look at the options:

(A) ozone is formed in the atmosphere from
(B) ozone is formed in the atmosphere when
(C) ozone is formed in the atmosphere, and when
(D) ozone, formed in the atmosphere when
(E) ozone, formed in the atmosphere from

Options D and E are fragments and when we substitute it back into the sentence, we can see that there is no main verb.

We can eliminate Options D and E

The correct idiomatic structure here is formed… when.

Option B is the best choice.

Hope this helps!

The answer to this question must be B:

A. This answer choice is correct until we hit the word "from." This last word must introduce a subordinate clause because "hydrocarbons and nitrogen oxides" becomes the subject of the next clause - this subject agrees with the plural verb "react."

B. This is the correct answer choice and the meaning is clear. "When" introduces the subordinate clause.

C. The comma + coordinating conjunction splits the meaning of the sentence. The meaning of the sentence is that ozone is formed because hydrocarbons and nitrogen oxides react with sunlight. However, this sentence splits the elements into separate thoughts. This is confusing.

D. Firstly, without a verb here, the sentence is a fragment. Also, the initial modifier doesn't seem to modify anything - it may seem to modify ozone, but the modifier should modify a clause or the subject of the clause.

E. Same as E. However, in this case, "from" is also incorrect.

Guys, I discarded option 'B' just because it's using 'when' ... I am under impression that 'when' is used only to refer time. Can you please help me understand this?

Dear Friends,

Here is a detailed explanation to this question-

Meaning is crucial to solving this problem:
Understanding the intended meaning is key to solving this question; the intended core meaning of this sentence is that ozone is formed in the atmosphere when hydrocarbons and nitrogen oxides react with sunlight.

Concepts tested here: Meaning + Grammatical Constructions

A:
1/ The sentence formed by this answer choice alters the meaning of the sentence through the phrase "from hydrocarbons and nitrogen oxides...react with sunlight"; the use of "from" leads to an incoherent meaning; the intended meaning is that ozone is formed in the atmosphere when hydrocarbons and nitrogen oxides react with sunlight.

B: Correct.
1/ This answer choice correctly acts upon the subject noun "ozone" with the active verb "is formed" to produce a complete thought, leading to a complete sentence.
2/ The sentence formed by Option B use the phrase "when hydrocarbons and nitrogen oxides...react with sunlight", conveying the intended meaning - that ozone is formed in the atmosphere because hydrocarbons and nitrogen oxides react with sunlight.

C:
1/ The sentence formed by this answer choice alters the meaning of the sentence through the phrase "and when hydrocarbons and nitrogen oxides...react with sunlight"; the construction of this sentence incorrectly implies that ozone is formed in the atmosphere and as a separate action, ozone is also formed when hydrocarbons and nitrogen oxides react with sunlight; the intended meaning is that ozone is formed in the atmosphere because hydrocarbons and nitrogen oxides react with sunlight.

D:
1/ This answer choice fails to form a complete sentence; as "formed" is a past participle acting as a noun modifier, there is no active verb to act upon the subject noun "ozone".

E:
1/ This answer choice fails to form a complete sentence; as "formed" is a past participle acting as a noun modifier, there is no active verb to act upon the subject noun "ozone".

Hence, B is the best answer choice.

All the best!
Experts' Global Team

Often visible as smog, ozone is formed in the atmosphere from hydrocarbons and
nitrogen oxides, two major pollutants emitted by automobiles, react with sunlight.

=>

ozone is formed in the atmosphere from hydrocarbons and nitrogen oxides react with sunlight.

(A) ozone is formed in the atmosphere from Sentence ends leaving react with sunlight dangling
(B) ozone is formed in the atmosphere when
(C) ozone is formed in the atmosphere, and when when hydrocarbons and nitrogen oxides react with sunlight what happens?
(D) ozone, formed in the atmosphere when What about ozone thus formed?
(E) ozone, formed in the atmosphere from Although it wouldn't make sense, this could be correct if react were reacts.

If anyone picked A in this question, it must have been because he/she didn´t read the whole question.

This is a simple problem, but Gmat usually uses this pattern of placing what it looks like a correct answer if you don´t read the entire sentence.


OA = B
Ozone is formed when h and n react with sunlight.

If you ignored the underlined portion = A
Ozone is formed from h and n ("yeah, this sounds right... Stop reading and move on")

option D

"ozone, formed in the atmosphere when"

why is this a sentence fragment ? cant the line "formed in the atmosphere when" be a ed modifier which modifies ozone ?

It is precisely because ‘formed in the atmosphere’ is a modifier, D is a fragment. As you may see, the Ozone is subject of the main clause but it lacks an appropriate verb, since ‘formed’, is not a verb but a past participle. Immediately after the modifier, a subordinate clause introduced by ‘when’ starts and the subject of the main clause is left dangling without a verb.

Often visible as smog, ozone is formed in the atmosphere from hydrocarbons and nitrogen oxides, two major pollutants emitted by automobiles, react with sunlight.

(A) ozone is formed in the atmosphere from
(B) ozone is formed in the atmosphere when
(C) ozone is formed in the atmosphere, and when
(D) ozone , formed in the atmosphere when ==> Creates a fragment
(E) ozone , formed in the atmosphere from ==> Changes the meaning and creates a fragment