Correct Answer: 18

Octane is a saturated straight chain hydrocarbon containing 8 carbon atoms. It falls into the group of organic compounds known as alkanes which have the general formula C_nH_2n+2.

Therefore applying the formula: Octane has 8 carbon atoms so n=8,

Therefore the number of hydrogen atoms is 2(8)+2 = 18.

Answering the Question:

For this question knowing the number of carbon atoms present in the molecule is most important. The name of the compound is a good indicator as to the number of carbon atoms present and the group of organic compound to which it belongs. Octo which is Latin for eight should be very familiar and is a good place to start. The suffix ane refers to the group of organic hydrocarbons called Alkanes. If you did not remember the general equation for alkanes then drawing the molecule and counting the hydrogen atoms is just as effective. We know the compound is saturated and as a result has only single bonds. We also know that carbon is capable of sharing the four electrons present in its outermost orbital.

We can therefore make a good guess as to the structure of octane, which is most likely;

CH₃-CH₂-CH₂-CH₂-CH₂-CH₂-CH₂-CH₃,

This would allow all the carbon atoms to have four bonds and be saturated by hydrogen. Counting the number of hydrogen (H) atoms we get the total number found in octane, which adds up to 18.