Answer:
A and C are different elements, while D is an isotope of C
Explanation:
To identify an atom, we simply use the atomic number. The atomic number is the number of protons in an atom.
For a neutral atom, the number of protons is the same as the number of electrons in such an atom.
Isotopes of an element have the same atomic number (protons) but different mass number(proton + neutron) as a result of their different number of neutrons.
From the given information about the atoms, only the second option is correct:
A and C are different elements because their atomic number differs:
A : 3 electrons, 3 protons and 3 neutrons
C : 4 electrons, 4 protons and 3 neutrons
D is an isotope of C:
C : 4 electrons, 4 protons and 3 neutrons
D : 4 electrons, 4 protons and 4 neutrons
They have the same atomic number but the mass number differs due to their different number of neutrons.
