Dr asked my mom to do root canel operation she is panic that whether any side effects occur if she do it!
Is it so any side effect occur if we do the root canel operation??

I have had 2 root canals before and never had any side effects. But that is not to say there aren't side effects here is a FAQ from dental-health about root canals.

Root Canals Ask The Dentist Questions about endodontic root canal procedures Dental Health Library

Worst side effect is that it's unsuccessful. I know. Had one and it went from a Maryland bridge to dental implant. Love the implant.

It's a relatively painful dental procedure (when the novocain wears off) and may have to be done in multiple visits. Not as bad as "crown lengtening" or "Jaw bone lowering" surgery.

KISS is correct, the worst side affect is that the root canal fails and the tooth needs to be removed.

Pain or discomfort varies from person to person. If your mom takes an anti-inflammatory like Advil before the treatment and another 6 hours later she will probably feel no or little discomfort when the freezing comes out. Most people find that the site where the injection was is more tender than the tooth that had the root canal. Be sure the dentist who does the root canal uses a rubber dam to isolate the tooth and prevent bacteria from entering the tooth while being treated.