It’s legal to use vex IQ parts like gears, chains, and plates in a VRC Robot?
No. If you read the game manual, page 25, rule (R5)C: c. Products from the VEXpro, VEX IQ, or VEX Robotics by Hexbug product line cannot be used for robot construction, unless specifically allowed by a clause of <R7>. Products from the VEXpro or VEX IQ, or VEX Robotics by Hexbug product line which are also cross listed as part of the VEX product line are legal.
The exception would be parts that are the same for IQ and EDR. For example axles are the same and for some packs the IQ ones are cheaper.
Ironically you can use vexIQ parts on an FTC robot but not VRC.
You can use them in this manner:
You can only use IQ pins to join together the license plates. But screws look much nicer
Oh! Thank you for the information, I need to read the rules again 
I’m going to theorize that this is a phrase that Karthik wishes you all of would say and followup on during the season. Lets all get together an make a huge attempt to not see posts that start “Well if you look at rule …”
That’s true, I was participating in Vex U, and now I will help a High School team, but some rules are different… Thanks for the help