[w451208]

Could someone explain why these answers are the way they are? Especially number 11. What is the best way to determine the answer without wasting to much time.

[AC Prabakar]

Just count the number of (i)hetero atom attached to the carbon(consider each bond as one count-for ex. double bond  gives two count)(ii) number of the bonds of the carbon (consider each bond as one count-for ex. double bond  gives two count).
Sum of these two will give u the oxidation level.
Arranging this number in ascending order will give u the answer.
U can check it out for the above example also...

I hope u r well aware of oxidation state and level..

[cth]

For question 11, I am surprised with answer A. 
I found the oxidation numbers to be:

picture      I      II     III
ox. nb.     +1    +2     0

So I think it is the answer D instead.

http://en.wikipedia.org/wiki/Oxidation_state

Just count the number of (i)hetero atom attached to the carbon(consider each bond as one count-for ex. double bond  gives two count)(ii) number of the bonds of the carbon (consider each bond as one count-for ex. double bond  gives two count).
Sum of these two will give u the oxidation level.

Sorry but I am not sure I understand what you meant: (ii) number of the bonds of the carbon (consider each bond as one count-for ex. double bond  gives two count)
Taken like that, a carbon atom always has four bonds (except for a few special cases such as carbanions,...). That way of calculating oxidation numbers looks erroneous for me.

[AC Prabakar]

Ohh!!!
Pls check the difference between "oxidation state" and "Oxidation level".
I am talking about oxidation level not about oxidation state.
The question no 11 also about oxidation level!!!!

Of course Oxidation number of all the carbon in question no 11 is "+4" i.e. same, but not oxidation levels are same.

Pls follow the following link for further details on oxidation levels:

http://www.chemicalforums.com/index.php?topic=24299.0

If u r having "Organic chemistry" by Clayden and warren-book refer chapter-2 p.No-35-37