Turning an affirmative statement into a question

Question

Are the budget airlines in a different strategic group than the major network airlines?

Is it a correct sentence? If I rewrite this sentence in an affirmative form, it could be

The budget airlines are in a different strategic group than the major network airlines.

But my question is about after linking verb are (before preposition in) whether something is required or not?

My question is about whether something is required between the words are and in. If I say:

I'm better at English than Karim.

that would be a correct sentence. But if I say

I'm _______ at English than Karim

then a question arises:

I'm ... what? ... at English than Karim.

Something, I mean an adjective (like better), is required between am and at.

Answer 1

When you change the sentence from a question to a statement, nothing is required between 'are' and 'in'. As you know, the word order is what determines whether it is a question or not.

You can add an adverb between the verb and preposition if needed.

The budget airlines are often in a different strategic group ...

The budget airlines are always in a different strategic group ...

But that will change the meaning of the sentence at least a little.

Answer 2

The affirmative sentence is in SVO order (well, SVC order because to be is a linking verb, but the distinction between an object and a complement is not important here).

As is common with a question, you have shifted it to VSO order.

The verb is are, the subject is the budget airlines, and the complement is "in a different strategic group than the major network airlines".

This a completely normal case of changing word order to make something a question. It needs no special treatment. You have thus formed the question correctly.