In order to understand this question and to answer it correctly, there are some definitions/terms that need to be acknowledged.
Firstly, TEMPERATURE is defined as the average KINETIC ENERGY of a sample. So, in the question when the reference is made to the speed of the molecules, it can be translated to temperature. Thus, since the speed of the molecules decreases, then it can be said that the Temperature of the system decreases.
Secondly, according to Gay-Lussac Law, Pressure is directly proportional to Temperature when the volume is constant. As such, an increase in Pressure sees an increase in Temperature.
Based on what is known above, the statement "In a rigid container, when the speed of the gas molecules decreases, the pressure of the gas also decreases" is a true one.
Thus the answer is TRUE.
