Chlorine with mass numbers 35 and 37 are isotopes of the same element, chlorine. Although they have the same number of protons (17) and electrons (17), they differ in the number of neutrons (18 and 20, respectively). This difference in neutron number does not affect the chemical properties of the element, including its valency.

Valency is determined by the number of valence electrons, which are the electrons in the outermost shell of an atom. Chlorine has seven valence electrons, which means it has a valency of 7. This valency remains the same for both chlorine-35 and chlorine-37 because they both have the same number of valence electrons.

Therefore, chlorine of mass number 35 and 37 will have the same valency of 7 and will exhibit similar chemical properties.