GENERAL KNOWLEDGE

Detailed explanation-1: -The mass number (symbol A, from the German word Atomgewicht [atomic weight]), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.

Detailed explanation-2: -The mass number of an atom is equal to the number of protons plus the number of neutrons that it contains. In other words, the number of neutrons in any atom is its mass number minus its atomic number. Although all atoms of a given element must have the same atomic number, they need not all have the same mass number.

Detailed explanation-3: -The number of protons is the atomic number, and the number of protons plus neutrons is the atomic mass.

Detailed explanation-4: -The nucleus, with its four protons and five neutrons, is surrounded by a cloud of electrons. In 1911, Ernest Rutherford discovered that at the core of every atom is a nucleus.

Detailed explanation-5: -The mass number is equal to the sum of the number of protons and the number of neutrons. So, the mass number of the given species is 81 (35 + 46). The element with the atomic number 35 is bromine (Br).