WHY DNA DOES NOT HAVE URACIL , AND RNA DOES NOT HAVE THYMINE ??

Dear student

Please refer the solution below for the said query

The presence of Thymine in place of Uracil in DNA confers it additional stability. 

Thymine is more stable (resistance to mutation) than uracil that is why it is present in DNA. Since DNA has to be stable, hence to accomplish these things, thymine is a component of DNA while uracil is present in RNA that adds to its instability. 

Hope this information clears your doubt about the topic.

Regards