when does the status of N/O and N/C contact of an output coil get updated

During program scan, if an external input changes, it is not noticed by the PLC till the next scan. Similarly, status of external outputs are modified only after the end of the program scan. Now, if an output is also being used as input contacts, then will the change in output image file be immediately noticed by the remaining rungs of the same scan, or will the status of corresponding N/O and N/C contacts change in the next scan?

The state of the output bit in the image file will be 'noticed' by the rungs which are immediately after the output instruction.

sinha_nsit said:

During program scan, if an external input changes, it is not noticed by the PLC till the next scan. Similarly, status of external outputs are modified only after the end of the program scan. Now, if an output is also being used as input contacts, then will the change in output image file be immediately noticed by the remaining rungs of the same scan, or will the status of corresponding N/O and N/C contacts change in the next scan?

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You assume too much, and the answer is platform dependent.

Some PLC's synchronize the I/O scan to the main (cyclic) program scan. Some do not. Where the platform uses asyncronous I/O scans, the state of an input may change from one network to the next.

GENERALLY, the internal state of logic referencing physical I/O is consistent within a program scan, but actually, it does not have to be. In most cases, the state of a physical output element will be properly represented in following logic, but really, that is not guaranteed.

Also, there is the possibility of a 'third party' communications process trying to steal control of I/O, which may or may not show up in the cyclic scan of logic. This is a bad practice, but I've seen done.