The mass number is 11. Hence, option C is correct.
An atom consists of a central nucleus that is usually surrounded by one or more electrons.
Mass Number(A) = Number of Protons + Number of Neutrons
The nucleus of an atom has 5 protons and 6 neutrons than the mass no. will be 6+5 = 11.
Hence, option C is correct.
Learn more about an atom here:
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