The valency is equal to the number of protons or number of electrons. Since number of protons and electrons are same in both chlorine 37 and chlorine 35, they will have same valency.
Chlorine 37 and chlorine 35 are isotopes of each other. Hence, they have same atomic number but different mass number.
The difference in their mass numbers is due to the different number of neutrons present in them.
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