How many different elements are represented by the nuclei in the table

B. 2

Explanation:

It's important to know what distinguishes an element and also the role that each sub particle of an atom plays. Understanding the concept of isotopes would be your way out in this particular question.

So what are isotopes?

Isotopes are simply atoms of an element with the same atomic number (number of protons) with different number of mass number (sum of number of protons and neutrons). This means the difference between isotopes are the number of neutrons but they are all atoms of the same element.

Examples of isotopes of Hydrogen include; Protium (Number of neutron = 0), Deuterium(Number of neutron = 1) and Tritium (Number of neutron = 2).

So we now unnderstand that what differentates element is the number of portons and not the neutrons. Back to the table, the atoms have two different number of protons ( 6 and 7). This means the correct option is B. 2