Question

The nucleus of an atom of cobalt-58 contains(1) 27 protons and 31 neutrons(2) 27 protons and 32 neutrons(3) 59 protons and 60 neutrons(4) 60 protons and 60 neutrons

Answer 1

The number next to cobalt (58) represents the atomic mass.
The atomic mass consists of protons and neutrons.
We know that the atomic number = # of protons.
 
- Look at a periodic table to find Cobalt's atomic number which is 27, meaning there are 27 protons.
-To find the number of neutrons, take 58-27 = 31 neutrons.

Therefore the answer is (1) 27 Protons and 31 Neutrons