Which of the following pairs of compounds are not position isomers ?

What are position isomers ?
They are the one with same molecular formula ,same  functional group and same carbon chain except the position of functional groups is different.

-COOH is the main functional group and numbering needs to be started from C of the -COOH
So in  c) example position of the -COOH is not changing.It is number one in both structures on the cabon chain of three carbons.

Its a great explanation (c) is correct answer thanks.