Given that a natural sample of iron $(Fe)$ has isotopes $_{26}^{54}Fe$,$_{26}^{56}Fe$,and $_{26}^{57}Fe$ in the ratios of $5\%$,$90\%$,and $5\%$ respectively. What will be the average atomic mass of iron $(Fe)$ (in $u$)?

Write two differences between isobars and isotopes.

Write the conclusions drawn by Rutherford for the following observations during his $\alpha$-scattering experiment:
$(a)$ Most of the alpha particles passed straight through the gold foil.
$(b)$ Some alpha particles got deflected from their path.
$(c)$ $A$ very small fraction of alpha particles got deflected by $180^{\circ}$.

$(a) (i)$ Name the scientist who proposed this model of the atom.
$(ii)$ Write the three postulates of this model.
$(iii)$ How many maximum electrons can be accommodated in the $M$ orbit?
$(b)$ What are canal rays? Give the characteristics of canal rays.

Will $^{35}Cl$ and $^{37}Cl$ have different valencies? Justify your answer.

The ion of an element has $3$ positive charges. The mass number of the atom is $27$ and the number of neutrons is $14$. What is the number of electrons in the ion?