The given statement is:

(A): The thermal efficiency of a regenerative Rankine cycle is always higher than that of a cycle without regeneration.
Reason (R): In regeneration cycle the work output is more.

To analyze this statement, let's break it down and evaluate each part individually.

Thermal Efficiency of a Regenerative Rankine Cycle:
The thermal efficiency of a power cycle represents the ratio of the net work output to the heat input. In the case of a regenerative Rankine cycle, the cycle includes a regenerator or a feedwater heater, where the working fluid is heated by the hot turbine exhaust gases before entering the boiler. This preheating process reduces the heat input required in the boiler, leading to an increase in the thermal efficiency.

Regeneration and Work Output:
The regenerative Rankine cycle utilizes a regenerator or a feedwater heater to recover some of the heat from the turbine exhaust gases. This recovered heat is then used to preheat the working fluid before it enters the boiler. By transferring heat from the exhaust gases to the feedwater, the temperature of the feedwater entering the boiler increases, reducing the heat input required to reach the desired steam conditions. This reduction in heat input leads to a decrease in the energy required to produce a given amount of work, resulting in a higher work output.

Now, let's evaluate the given options:

a) Both A and R are individually true and R is the correct explanation of A:
This option suggests that both the statement and the reason are true, and the reason correctly explains the statement. However, this is not the correct answer because the statement itself is not always true.

b) Both A and R are individually true but R is not the correct explanation of A:
This option suggests that both the statement and the reason are true, but the reason does not correctly explain the statement. This is a plausible answer, as the reason provided is not the only factor contributing to the higher thermal efficiency of a regenerative Rankine cycle.

c) A is true but R is false:
This option suggests that the statement is true, but the reason is false. This is the correct answer because the statement itself is not always true. The thermal efficiency of a regenerative Rankine cycle can be higher or lower than that of a cycle without regeneration, depending on various factors such as the design and operation parameters.

d) A is false but R is true:
This option suggests that the statement is false, but the reason is true. This is not the correct answer as the statement itself can be true in certain cases, although it is not always true.

In conclusion, option 'C' is the correct answer as the statement is not always true, and the reason provided is false. The thermal efficiency of a regenerative Rankine cycle can be higher or lower than that of a cycle without regeneration, depending on various factors.