Which nitrogen base is missing in the DNA and RNA?

No nitrogen base is missing. You may be referring to the fact that DNA contains the nitrogen base thymine, while RNA contains the nitrogen base uracil. They both contain adenine, cytosine, and guanine.
No nitrogen base is missing. You may be referring to the fact that DNA contains the nitrogen base thymine, while RNA contains the nitrogen base uracil. They both contain adenine, cytosine, and guanine.