Chemistry

Chemical properties of an element are primarily determined by the number and arrangement of its electrons. Isotopes of the same element have the same number of protons, and in a neutral atom, they also have the same number of electrons. This identical electron configuration leads to virtually identical chemical behavior.

While there can be very subtle differences in reaction rates due to the mass difference (kinetic isotope effects), for most practical purposes and in general chemistry, isotopes of the same element are considered to have the same chemical properties.

Protium (¹$H₁$), Deuterium (²$H₁$ or D), and Tritium (​³H₁ or T) are the naturally occurring isotopes of  Hydrogen.

All three have the same atomic number (1), meaning they each have one proton. However, they differ in their number of neutrons:

Protium: 0 neutrons
Deuterium: 1 neutron
Tritium: 2 neutrons

This difference in neutron number leads to their different mass numbers (1, 2, and 3 respectively).

Deuterium (an isotope of Hydrogen): 1 proton, 1 neutron.

Iodine (most common isotope Iodine-127): 53 protons, 74 neutrons ($127-53=74$).  

Chlorine (most common isotope Chlorine-35): 17 protons, 18 neutrons ($35-17=18$).

Therefore, (b) Deuterium has an equal number of neutrons and protons.