Amolecule of pentane is made of 5 carbon atoms and 12 hydrogen atoms. a collection of pentane molecules has 3.01 x 1024 carbon atoms. how many hydrogen atoms are in the collection? 3.01 × 1024 × (12/5) hydrogen atoms (3.01 × 1024 / 5) hydrogen atoms 3.01 × 1024 × (5/12) hydrogen atoms 3.01 × 1024 × 12 hydrogen atoms description

3.01 Ă— 10^24 Ă— (12/5) hydrogen atoms  
Looking at the formula for the molecule, the ratio of carbon to hydrogen atoms is 5:12, so if we divide the number of carbon atoms by 5 and then multiply by 12, we can find the number of hydrogen atoms. Let's look at the available options and see what makes sense.  
3.01 Ă— 10^24 Ă— (12/5) hydrogen atoms 
* This is exactly correct.  
(3.01 Ă— 10^24 / 5) hydrogen atoms 
* Nope. This will tell you how many pentane MOLECULES you have, but not the number of hydrogen atoms.  
3.01 Ă— 10^24 Ă— (5/12) hydrogen atoms 
* Close, but the ratio (5/12) will tell you the number of carbon atoms you have if you give it the number of hydrogen atoms. So this choice is wrong.  
3.01 Ă— 10^24 Ă— 12 hydrogen atoms description 
* This would tell you the number of hydrogen atoms you have if you know the number of pentane molecules you have. So this choice is also wrong.