Question

Which of the following elements contain the greatest number of atoms?
(A) 4g He
(B) 46g Na
(C) 0.40g Ca
(D) 12g He

Answer 1

Hint : To answer this question, we first need to understand what are elements. An element is a pure substance made up entirely of atoms with the same number of protons in their atomic nuclei, as defined by chemistry. Chemical elements, unlike chemical compounds, cannot be broken down chemically into simpler molecules.

Complete Step By Step Answer:
Atoms – The smallest unit of ordinary matter that makes up a chemical element is an atom. Atoms that are neutral or ionized make up every solid, liquid, gas, and plasma. Atoms are incredibly small, measuring about 100 picometers in diameter.
Moles - A mole is defined as $6.022 \times {10^{23}}$ atoms, molecules, ions, or other chemical units. Because of the large number of atoms, molecules, and other particles in any substance, the mole is a convenient quantity to employ.
Molar mass of He- 4 grams
Molar mass of Na – 23 grams
Molar mass of Ca - 40 grams
$number{\kern 1pt} {\kern 1pt} of{\kern 1pt} {\kern 1pt} moles = \dfrac{{mass{\kern 1pt} {\kern 1pt} of{\kern 1pt} {\kern 1pt} element}}{{molar{\kern 1pt} {\kern 1pt} mass}}$
So, number of moles in each case
Moles of He $= \dfrac{4}{4} = 1{\kern 1pt} {\kern 1pt} mole$
Moles of Na $= \dfrac{{46}}{{23}} = 2{\kern 1pt} {\kern 1pt} moles$
Moles of Ca $= \dfrac{{0.40}}{{40}} = 0.1{\kern 1pt} {\kern 1pt} mole$
Moles of He $= \dfrac{{12}}{4} = 3{\kern 1pt} {\kern 1pt} mole$
As we know that number of moles are directly proportional to number of atoms
So higher the number of moles more the number of atoms
We get that 12 grams of helium has the highest number of moles so then it will also have the highest number of atoms
So, the final answer is option (D) i.e., 12g He.

Note :
The mass of a sample of a chemical compound divided by the amount of material in that sample, measured in moles, is the molar mass of that compound in chemistry. It refers to the mass of one mole of a material.