1. C  - Electrons are not found in the nucleus.  A nucleus is made up of protons and neutrons.  

​

2. (12)(0.9893) + (13)(0.01078) = 12.01

​

Carbon-14 exists, and is necessary for a process called "Carbon Dating", but its concentration is 0.000 000 000 1% so it doesn't change the value of the calculation.