Question about "이거 뭐예요?"

I have questions. 

이거 뭐야?

이거 뭐예요?

이것은 뭐예요?

그거 뭐예요? 

저거 뭐예요? 

저것은 뭐야?

1) I want to know if these mean the same thing?

2) Or If I can use them in in any situation?

3) Or does it depend on the situation? 

<My answer>

1) 이거 뭐야?

2) 이거 뭐예요?

3) 이것은 뭐예요?

4) 그거 뭐예요? 

5) 저거 뭐예요? 

6) 저것은 뭐야? 

1. all of 1) 2) 3) means "What is this? / What are these?"

* 이거 is a short form of 이것은 <— 이것(this or these) + 은(주격조사 : a prepostion makes a noun subjective)

* 이것 is often used as a form of 이거 because 이것은 is dificult to be pronounced. 이것 is changed into 이거 and 은 is oniitted because Korean people often omit prepositison if other can understand.

* 뭐 is a short form of 무엇 and is an informal style, 무엇 is a formal style.

* 뭐예요 is said to anybody <— 뭐(what) + 예요(a short form of 이에요 and a little polite verb ending suffix)

* 뭐야 is to the younger or friendly like your friends or family <— 뭐(what) + 야(a question suffix to the younger or friendly)

2. Explanation about 4) 5) 6)

* 그거 is a short form of 그것은<— 그것(that or it) + 은(주격조사 : a prepostion makes a noun subjective)

* 그것 is often used as a form of 그거 because 그것은 is dificult to be pronounced. 그것 is changed into 그거 and 은 is oniitted because Korean people often omit prepositison if other can understand.

* 저거 is a short form of 저것은<— 저것(that over there) + 은(주격조사 : a prepostion makes a noun subjective)

* 저것 is often used as a form of 저거 because 저것은 is dificult to be pronounced. 저것 is changed into 저거 and 은 is oniitted because Korean people often omit prepositison if other can understand.

3. Polite attitudes.

* You can say 2) 3) 4) 5) to anybody. but if the other is the elderly you had better say 무엇입니까? instead of 뭐예요 bcz 무엇입니까? is much polite.

* You can say 1) 6) only to the younger or your friends or your family like siblings or brothers bcz 뭐야 is not polite.