Balancing a reaction need help ?

Any particular song?

How 'bout CC Rider. 

When in doubt Charley out. The answer is C.

There are two aspects: you have to check atom number conservation in these chemical reactions (for example, if there are 8 carbon atoms on the left-hand side, there must also be 8 carbon atoms on the right-hand side as well).

Reactions A and C satisfy these conditions (for example, there are 18 hydrogen atoms on both sides of reaction A), reactions B and D do not.

You must also check that the molecules do exist. In reaction A, molecule H18 O does not exist, so this reaction is ruled out. The only real reaction is reaction C, like Dr W and Bill said.

this is a typical combustion reaction which produces H2O and CO2

.. __ CxHy + __ O2 ---> __ CO2 + __H2O

let's balance.  we know x and y and let's swap CO2 and H2O

.. __ C8H18 + __ O2 ---> __ H2O + __ CO2

so we begin by choosing an element on the left that appears in 1 reactant and is not H nor O if possible.  That leaves "C" carbon.  We then choose an integer to place in front of the reactant containing that element.  Usually we want to chose, 1, 2, 3, or 4.  In this case, I'll demonstrate what happens if we choose "1".  We place that "1" in front of the reactant containing our "C"

.. 1 C8H18 + __ O2 ----> __ H2O + __ CO2

balancing C on the right.  let's see we have 1 x 8 = 0 on the left, we need 8 on the right.  Since each CO2 has 1, the coefficient of CO2 must be 8

.. 1 C8H18 + __ O2 ----> __ H2O + 8 CO2

next balancing H.  1x18 = 18 on left, we need 18 on right

.. 1 C8H18 + __ O2 ----> 9 H2O + 8 CO2

next we balance O's.. 9x1 + 8x2 = 25 on the right, so we need 25 on the left 

.. 1 C8H18 + 25/2 O2 ---> 9 H2O + 8 CO2

we double everything to get rid of the fraction

.. 2 C8H18 + 25 O2 ---> 18 H2O + 16 CO2

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"C" is the correct choice

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Something for YOU to try.  Chose "2" as your starting integer and see if you get the same result. 

Answer is C because 

C8H18 + O2 => H2O + CO2

C8H18 + 12.5O2 => 9H2O + 8CO2

Because this is not possible

2C8H18 + 25O2 => 18H2O2 + 16CO2

This can be verified as there are the same amount of parts on the Left Hand Side as the Right. I am no chemistry teacher so my explanation is a bit trash