Which of the following situations would cause the greatest decrease in the motion of molecules in a system?
a. q = -50 j, w = -50 j
b. q = +50 j, w = +50 j
c. q = -50 j, w = +50 j
d. q = +50 j, w = -50 j

Option A

Explanation: Now, i will consider that W and A refers to the work and heat done/applied to the system  

Always Q is related to the heat, so if Q is positive this means that the temperature of the system increase if Q is negative this means that heat is extracted from the system, and the temperature decreases, which implies that the motion of the particles decreases.

For the work is the same, if the applied work is positive, then the energy of the system increments (suppose a gas inside a piston, if you compress the piston the work is positive, and now the particles are close together, wich increments the temperature of the gas)

If the work is negative, this means that the system does the work, so the energy decreases, and also the motion of the particles, so the correct option A