So now is there a way to debug each blocks I mean I want to see whether the particular function is being called or not (even if its an inbuild function also)
What you typically do is use DoIt, to execute a particular block or to see the value of a specific variable. (search the FAQ for instructions if you do not know how to do it).
Or, for events happening quickly, put some (temporary) labels on your UI. Every time an event happens, add some interesting values to that label. If you are finished with the label, delete it or make it invisible.
That is the power of App Inventor!
In addition to Ghica's comments, perhaps these links will help
https://ai2.appinventor.mit.edu/reference/other/testing.html