How do I know if my egg is rotten??

[Chickens of the century]

I opened an egg after its hatching date and found it fertilized but with a lot of yolk and liquid and it was very hollow. Does that mean it's rotten?

 

[LizGio]

If it incubated for 21 days and there was nothing going on it was a dud. It may or may not have been fertilized. Sometimes things just don't work out.

 

[Chickens of the century]

Thanks for your advice!