See how the carbon chains are numbered. Correct the wrong ones.

a)

b)

c)

d)

a.

The carbon atoms are numbered correctly in the above structure.

b.

The carbon atoms are not numbered correctly in the above structure. The correct numbering is as shown in the following picture: -

The numbering is done so as to choose the longest branch of carbon and giving the carbon bearing the substituent the lowest number possible.

c.

The carbon atoms are not numbered correctly in the above structure. The correct numbering is as shown in the following picture: -

The numbering is done so as to choose the longest branch of carbon and giving the carbon bearing the substituent the lowest number possible. Here two ways of numbering are there as shown in the structures above but either way we get the same length of the main chain and position of the two substituents. Hence, any one of the way can be chosen for numbering the chain.

d.

The carbon atoms are not numbered correctly in the above structure. The correct numbering is as shown in the following picture: -

The numbering is done so as to choose the longest branch of carbon and giving the carbon bearing the functional group the lowest number possible.