A. the carbons are unbalanced
B. the hydrogens are unbalanced.
D. the chlorines are unbalanced.
That leaves C. to be correctly balanced.
maximum allowed value of the speed in roller coaster is given as

now from kinematics we can say

here initial speed will be

acceleration is due to gravity

now we can use this to find the height



so maximum allowed height will be 20.4 m