There are two different substances with the formula c5h10 that contain a 5-carbon chain. draw them.

Explanation:

Above Formula has C5H10.

So Calculated Hydrogen =  12

    The actual hydrogens =  10

                       difference = 12-10 = 2

Degree of Unsaturation = 2/2 = 1

So there is possibility of one double bond.        

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

the answer is definitely c.