# Question #d7e9b

##### 1 Answer

The sample that contains

#### Explanation:

Notice that the problem asks you which sample contains the same **number of atoms** as **molecules**, *not* atoms.

Keep this in mind.

Also, it's worth noting that you're looking for how many **moles** of atoms are present in the samples. That is the case because a *mole* is simply a very large collection of atoms.

If you know how many *moles* of atoms you have, you **automatically** know how many atoms you have.

So, the problem provides you with a mass of hydrogen gas and the **molar mass** of the gas, which means that you can calculate how many **moles** of hydrogen gas are present in your sample

#1 color(red)(cancel(color(black)("g"))) * "1 mole H"_2/(2 color(red)(cancel(color(black)("g")))) = "0.5 moles H"_2#

Now, **every mole** of hydrogen gas contains **mole** of *hydrogen atoms*, since

#0.5 color(red)(cancel(color(black)("moles H"_2))) * "2 moles atoms"/(1 color(red)(cancel(color(black)("mole H"_2)))) = "1 mole atoms"#

This means that you're looking for the sample that contains **exactly** **mole** of atoms.

At this point, it should become clear that the answer is **(c)**. You're dealing with **molar mass** of

This, of course, implies that the third sample contains

#20 color(red)(cancel(color(black)("g"))) * "1 mole Ne"/(20color(red)(cancel(color(black)("g")))) = "1 mole Ne"#

You can check the other samples if you want to make sure that the question does not have *multiple* answers. I'll show you how to do the first one.

For carbon dioxide,

#22 color(red)(cancel(color(black)("g"))) * "1 mole CO"_2/(44color(red)(cancel(color(black)("g")))) = "0.5 moles CO"_2#

But **every mole** of carbon dioxide contains **moles** of atoms, i.e.

#0.5 color(red)(cancel(color(black)("moles CO"_2))) * "3 moles atoms"/(1color(red)(cancel(color(black)("mole CO"_2)))) = "1.5 moles atoms"#

You can use the same approach to see that sample **(c)** is indeed the only one that contains the same number of moles at the sample of hydrogen gas.

And remember, a **mole** is just a fixed number,