sentence construction - Which of the questions is correct?

I have given my view why I think each of them may be correct.

1) Why is the young Joe right handed but the old Joe left handed?

In example 1, I think there is no need to add "is" two times ie."young Joe is right handed but the old Joe is left handed?" and that is why a single "is" would suffice.

2) Why is the young Joe right handed but the old Joe is left handed?

Here I have taken only the first "is" ie from "..young Joe is right handed..." to make the question. So the second "is" should be retained in its proper place.

3) Why is it that the young Joe is right handed but the old Joe left handed?

I think this question is okay, but need to ascertain it.

4) Why is young Joe is right handed but the old Joe is left handed?

I have retained both "is"; just added an extra "is" to make a question.

Now I am confused on the correctness of these constructions. These constructions just flowed through my head, but a long divorce with Grammar books made me feel doubt regarding them. Please elaborate which of the above is correct and which is not?

Answer

Because you are talking about people, you should start the name 'joe' with an upper case letter. I would also shy away from having a 'the' in front of young or old. Young Joe (or old Joe) works as an identifier and doesn't carry an inference of turning people into things. Apart from that:

1) is fine when it is changed as above to:

Why is (the) young Joe right handed but (the) old Joe left handed?

You're correct in saying you don't really need an extra is between 'old Joe' and 'left handed'. It's not wrong, but it's unnecessary. Hence

2) isn't incorrect, but you don't need the italicised is and it makes it sound a bit odd

Why is (the) young Joe right handed but (the) old Joe is left handed?

3) in contradiction of 2), I would add the second 'is' to this one. Because of the addition of is it that, you have set up the alternate clauses differently.

Why is it that young Joe is right handed but old Joe is left handed?

4) is wrong. the 'Why is young Joe is ..' is not grammatically correct. The added is makes it make no sense.