1. Which is the number of neutrons in 35 80 Br

45

Explanation:

An atom consist of electron, protons and neutrons. Protons and neutrons are present with in nucleus while the electrons are present out side the nucleus.

All these three subatomic particles construct an atom. A neutral atom have equal number of proton and electron. In other words we can say that negative and positive charges are equal in magnitude and cancel the each other. For example if neutral atom has 6 protons than it must have 6 electrons. The sum of neutrons and protons is the mass number of an atom while the number of protons are number of electrons is the atomic number of an atom.

For example

The atomic number of bromine is 35 and atomic mass is 80 g/mol

The number of protons = 35

The number of electrons = 35

The number of neutrons = 80-35 = 45