Acceleration = (change in speed) / (time for the change)
Change in speed = (later speed) - (earlier speed) = (13 - 24) = -11 km/hr
Time for the change = 2 seconds
Acceleration = (-11 km/hr) / (2 sec)
Acceleration = -5.5 km/hr-sec (B)
Sublimation is the state shown in the model
I will say increasing temperature but you dont have that option on your list, so I would take B. Increasing Concentration.
You would expect to find the center of gravity in a ruler in the middle because if you were to cut a ruler in half, depending on the center of gravity, you would have two equal pieces, which mean there is equal weight, meaning the middle is the center of gravity