Find out the valency of an element $X$ having atomic number $16$.

The first model of an atom was given by

Which property of an element can be used for its identification?

Which of the following statements are true for an element?
$(i)$ Atomic number $=$ number of protons $+$ number of electrons
$(ii)$ Mass number $=$ number of protons $+$ number of neutrons
$(iii)$ Atomic mass $=$ number of protons $=$ number of neutrons
$(iv)$ Atomic number $=$ number of protons $=$ number of electrons

State whether the following statement is true or false:
The relative atomic masses of all elements have been found with respect to an atom of oxygen-$16$.

Which of the following in the figure do not represent Bohr's model of an atom correctly?