Which of the following contains the maximum number of molecules?

$(a)$ An atom is considered electrically neutral. Explain.
$(b)$ State the valency of Helium.
$(c)$ If an atom has an atomic mass of $4$ and $2$ protons in its nucleus,how many neutrons does it have?

As per the law of definite proportion,carbon and oxygen combine in the ratio of $3:8$. Compute the mass of oxygen gas that would be required to react completely with $15\,g$ of carbon.

Write the chemical names of the following compounds:
$(a)$ $K_{2}SO_{4}$
$(b)$ $Mg_{3}(PO_{4})_{2}$
$(c)$ $NH_{4}Cl$
$(d)$ $ZnS$
$(e)$ $Na_{3}N$
$(f)$ $AgBr$

$(a)$ What is the law of constant proportions? Explain with the help of an example.
$(b)$ Which postulate of Dalton's atomic theory is in agreement with this law?

$(a)$ Define the following:
$(i)$ Mole
$(ii)$ Gram atomic mass
$(iii)$ Gram molecular mass
$(b)$ Calculate the mass of the following:
$(i)$ $2$ moles of carbon dioxide
$(ii)$ $6.022 \times 10^{23}$ molecules of carbon dioxide.