The first model of an atom was given by

Which of the following statements about Rutherford's model of the atom are correct?
$(i)$ Considered the nucleus as positively charged.
$(ii)$ Established that the $\alpha$-particles are four times as heavy as a hydrogen atom.
$(iii)$ Can be compared to the solar system.
$(iv)$ Was in agreement with Thomson's model.

One electron is present in the outermost shell of the atom of an element $X$. What would be the nature and value of charge on the ion formed if this electron is removed from the outermost shell?

Write the symbols of two isotopes of uranium.

$(a)$ How many neutrons are present in $C-14$ isotope of carbon?
$(b)$ How many protons does $He^{2+}$ ion possess?
$(c)$ How many maximum electrons can be filled in the $3^{rd}$ orbit of an atom?
$(d)$ How many electrons does $He^{2+}$ ion possess?

Two elements are denoted as follows:
$_{20}^{40}A$ and $_{18}^{40}B$
$(a)$ Find the number of electrons present in $A$ and $B$.
$(b)$ Find the number of nucleons present in $A$ and $B$.
$(c)$ Explain the special 'term' used to represent $A$ and $B$ and define the same.