Which one of the following will have the highest number of atoms? 

The smallest piece of stuff that makes up a chemical element is an atom. Anything that takes up space and has a distinct mass is considered matter. The three states of matter—solid, liquid, and gas—that matter may exist in are known as states of matter.Every atom has a nucleus, which is made up of protons and neutrons with protons having a positive charge and neutrons having a neutral charge. Positively charged electrons are rotating around the nucleus.
We must compute the number of atoms in each element in order to determine which will have the most of them. One may compute the number of atoms step by step:
1. Determine the element's molar mass first.
2. Next, determine how many moles there are.
3. Use Avogadro's number to transform atoms into moles.$\text{Number of moles} =\frac{\text{Weight}}{\text{Gram atomic/Molecular mass}}$

The gram atomic mass of $\mathrm{Au}$ (Gold) = $197 \text{gm}$

The number of moles of $\mathrm{Au}$ $=\frac{1\text{g}}{197\text{g}}=\frac{1}{197}\text{mole}$

The gram atomic mass of $\mathrm{Na}$ (Sodium) $=23 \text{g}$

Number of moles of $\mathrm{Na}$ $=\frac{1\text{g}}{23\text{g}}=\frac{1}{23}\text{mole}$

The gram molecular mass of ${\mathrm{Cl}}_2$ (Chlorine gas) $=71 \text{g}$

Number of moles of ${\mathrm{Cl}}_2$ $=\frac{1\text{g}}{71\text{g}}=\frac{1}{71}\text{mole}$

Therefore, Lithium ($\text{Li}$) has the highest number of moles i.e. $\frac{1}{7}$.

Hence option (C) is correct.