Here, Your Expression: y = 0.25 (2^x)
So, we can see the expression is "Exponential" which increases double in every hour. So, the only graph with that pattern is 3rd one.You can compare following coordinates: (1, 50), (2, 100), (3, 200)
For every 1 value of x, y increases to it's double.
In short, Your Answer would be Option C
Hope this helps!