For what value of a is a probability density function?

Question

For what value of a is  a probability density function? ​

Quizplus · Accepted Answer

For a function to be a probability density function, it must satisfy two conditions: non-negativity and integration over the entire range of the variable being equal to 1. 
Looking at the options, we can see that the last 6 digits in each option represent the hexadecimal number for the value of a. Only option B has a value of a that provides a valid probability density function because when we integrate the function over its entire range, we get a value of 1. The other options either give a negative value for the function or do not integrate to 1.

For What Value of a Is a Probability Density