Hi vinay1976.
There are two main ways to check for parallelism.
One is to check to see whether sentence elements that should be parallel are of the same type.
Example:
John
fixed the bike,
tuned up the lawnmower, and
the dishwasher.
We see that the first two elements are verb phrases, but the third is just a noun phrase. So, the list isn't parallel.
We can also check for parallelism by analyzing the logic of the sentence.
John
fixed the bike, (John)
tuned up the lawnmower, and (John)
the dishwasher.
When we place the introductory element (John) before each element, we get "John the dishwasher." Since that doesn't make sense, the list isn't parallel.