An atomic mass unit equals A. The number of protons in the nucleus of each atom.
B. The mass of an electron.
C. The sum of the masses of protons and neutrons in an atom.
D. The mass of one proton or neutron.

C. The sum of the masses of protons and neutrons in an atom.

Explanation:

We know that an atom consist of electrons, protons and neutrons. Neutrons and protons are present inside the nucleus while electrons are present out side the nucleus. Electron has a negative charge and is written as e⁻. The mass of electron is 9.10938356×10⁻³¹ Kg . While mass of proton and neutron is 1.672623×10⁻²⁷Kg and 1.674929×10⁻²⁷ Kg respectively.

Symbol of proton= P⁺  

Symbol of neutron= n⁰  

The number of proton or number of electrons are called atomic number while atomic mass of an atom is sum of mases of protons and neutrons. An electrically neutral  atom always have equal number of protons and electrons and when an atom loses its valance electron the number of protons increases and thus positive charge increased and atom form cation.

the answer is definitely c.

the ratio of the conjugate base to the acid required to attain the desired ph.