"what is the concentration of positive charge and mass in rutherford's atomic model called? "

The concentration of positive charge and mass in Rutherford's atomic model is called the nucleus. Rutherford's experiments involving the use of alpha particle beams directed onto thin metal foils demonstrated the existence of the nucleus. The nucleus of an atom contains positively charge particles called protons and other uncharged particles called neutrons. According to this model most volume of an atom is made up of an empty space. 

C) electrons encircling a nucleus with neutrons and protons

There is no reason to think the results are biased or not conducted properly but you should not assume the results are correct just because they were done in a laboratory so the answer would be c. it is likely to be reliable because the results support the conclusion presented.