Answer :The mass number is 56.
Step-by-step explanation:
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons = 26+ 30 =56
Atomic number is defined as the number of protons or number of electrons that are present in an atom.
Atomic number = Number of electrons = Number of protons = 26
Hence, neutrons and protons affects the mass number and thus the mass number will be 56.