How is an atom represented? Why?

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(N/A) An atom is represented by the notation $^A_Z X$,where $X$ is the chemical symbol of the element,$Z$ is the atomic number (number of protons),and $A$ is the mass number (total number of protons and neutrons).
The positive charge in the nucleus is due to the protons. $A$ proton carries one unit of fundamental charge and is stable.
All the electrons of an atom are outside the nucleus and revolve around it in circular orbits due to the electrostatic Coulomb force.
The number of electrons in a neutral atom is equal to the atomic number $Z$. Hence,the total charge of the electrons is $(-Ze)$.
Since the atom is electrically neutral,the total positive charge of the nucleus must be $(+Ze)$. Therefore,the number of protons in the nucleus is equal to the atomic number $Z$.

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Choose the correct option from the following options given below.

Answer the following questions,which help you understand the difference between Thomson's model and Rutherford's model better.
$(a)$ Is the average angle of deflection of $\alpha$-particles by a thin gold foil predicted by Thomson's model much less,about the same,or much greater than that predicted by Rutherford's model?
$(b)$ Is the probability of backward scattering (i.e.,scattering of $\alpha$-particles at angles greater than $90^{\circ}$) predicted by Thomson's model much less,about the same,or much greater than that predicted by Rutherford's model?
$(c)$ Keeping other factors fixed,it is found experimentally that for small thickness $t$,the number of $\alpha$-particles scattered at moderate angles is proportional to $t$. What clue does this linear dependence on $t$ provide?
$(d)$ In which model is it completely wrong to ignore multiple scattering for the calculation of average angle of scattering of $\alpha$-particles by a thin foil?

The graph which depicts the results of the Rutherford gold foil experiment with $\alpha$-particles is:
$\theta$: Scattering angle
$Y$: Number of scattered $\alpha$-particles detected
(Plots are schematic and not to scale)

An alpha particle colliding with one of the electrons in a gold atom loses

Using Thomson's model of the atom,consider an atom consisting of two electrons,each of charge $-e$,embedded in a sphere of charge $+2e$ and radius $R$. In equilibrium,each electron is at a distance $d$ from the center of the atom. What is the equilibrium separation between the electrons?

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