Chemical behaviour of an atom is determined by

Isobars are atoms with

The number of electrons plus neutrons in ${}_{19}^{40} K^{+}$ is $.....$

If $W$ is the mass number and $N$ is the atomic number of an element,then:

What are $_{17}^{35}Cl$ and $_{17}^{37}Cl$? Why?

Assertion : The sum of protons and neutrons is always different in isobars.
Reason : Isobars are atoms of different elements having same mass number but different atomic number.