The rate of material __________ is zero in case of a steady state system.

ANS:A - accumulation

In a steady-state system, the rate of material accumulation is zero. A steady-state system is one in which the system's properties do not change over time, meaning that the system is in a state of balance where any changes occurring within it are offset by other changes so that overall, there is no net change. In such a system, the amount of material entering the system is equal to the amount leaving the system, resulting in a constant quantity of material within the system. Therefore, the correct answer is: accumulation. Accumulation refers to the process of a substance collecting or gathering over time within a system or a particular location within that system. It's essentially the increase in the amount or quantity of a substance within a specified area or volume. In various systems, accumulation can occur due to different reasons:

1. Input exceeds output: If the rate of input of a substance into a system is greater than the rate at which it leaves the system, accumulation will occur. For instance, in a bathtub with water flowing in faster than it drains out, water accumulates in the bathtub.
2. No output: If there is no output of a substance from the system, accumulation will occur even if the input rate is exactly balanced with the output rate. For example, in a closed container where air is being continuously pumped in but none is being let out, the concentration of air molecules will accumulate over time.
3. Reduced output: Sometimes, the output rate of a substance may decrease while the input rate remains constant. In such cases, accumulation can occur until a new equilibrium is reached.

In the context of a steady-state system, accumulation is non-existent because the system is in a state of balance where any changes occurring within it are offset by other changes so that overall, there is no net change. This means that the rate of material accumulation is zero in a steady-state system because the input rate is balanced by the output rate, resulting in a constant amount of material within the system.