A sample of sodium has a mass of $46g$. What is the mass of the same number of?
calcium atoms as sodium atoms present in a given sample?
(a) $46g$
(b) $20g$
(c) $40g$
(d) $80g$

Hint: first we have to find the moles of the sodium atom by using the formula as;
$mole=\dfrac{given\text{ }mass}{molecular\text{ }mass}$ and after that we can find the mass of the calcium atoms by multiplying the number of atoms with the molecular mass of the calcium. Now solve it.

Complete answer:
First of let’s discuss sodium and ethanol. Sodium is alkali metal which belongs to the s-block element and has the atomic number as 11 and the mass number as 23. It is very soft and so soft that it could be easily cut with a knife and in its outermost shell it has one electron and has a strong tendency to lose the electron to acquire the stable electronic configuration of the nearest noble gas i.e. the neon.
Sodium is alkaline-earth metal which belongs to the s-block element and has the atomic number as 20 and the mass number as 40. In its outermost shell it has two electrons and has a strong tendency to lose the electron to acquire the stable electronic configuration of the nearest noble gas i.e. the neon.
Now considering the statement as;
We have been given that the number of the calcium atoms is the same as that of the sodium atoms. So, first we will find out the no of atoms i.e. the moles of sodium.
Mass of sodium= $46g$ (given)
Molecular mass of sodium=$23$
Then, the no. of moles of sodium is as;
$\begin{align}
& mole=\dfrac{given\text{ }mass}{molecular\text{ }mass} \\
&\implies \text{ }\dfrac{46}{23} \\
&\implies \text{ 2} \\
\end{align}$
So, therefore, the no of sodium atoms present is 2.
Now, the mass of the calcium atoms can be calculated as;
$\begin{align}
& mass\text{ }of\text{ }calcium\text{ }atoms=2\times 40\text{ (molecular mass of Ca=40)} \\
&\implies \text{ 80g} \\
\end{align}$

Thus, the mass of the same number of calcium atoms as sodium atoms present in a given sample is $80g$.

Note: While doing the calculations, always keep in mind that the units of all should be same i.e. if the mass of the sodium atom is given in grams then, the mass of the calcium atom is also in grams and if it is given in kilograms, then mass of calcium atoms is also in kilograms.