Explanation:

In an air standard Brayton cycle, the maximum temperature of the cycle is a key parameter that affects the performance of the cycle. Let's analyze the effect of increasing the maximum temperature while keeping the pressure ratio the same.

Understanding the Air Standard Brayton Cycle:
The air standard Brayton cycle is a thermodynamic cycle that represents the idealized behavior of a gas turbine engine. It consists of the following four processes:

1. Isentropic Compression: The air is compressed from the initial state (Point 1) to a higher pressure (Point 2) in a compressor. This process is assumed to be isentropic, meaning no heat is added or rejected during compression.

2. Constant Pressure Heat Addition: The compressed air at Point 2 is then sent to the combustion chamber, where fuel is burned and heat is added at constant pressure. This process is represented by a vertical line on the temperature-entropy diagram.

3. Isentropic Expansion: The high-temperature and high-pressure air at Point 3 is expanded in a turbine, producing work. This expansion process is assumed to be isentropic.

4. Constant Pressure Heat Rejection: The air leaving the turbine at Point 4 is cooled to the initial state temperature through heat rejection in a heat exchanger. This process is represented by a vertical line on the temperature-entropy diagram.

Effect of Increasing Maximum Temperature:

When the maximum temperature of the cycle is increased while keeping the pressure ratio the same, the following changes occur:

1. Compression Process: The compression process is not affected by the increase in maximum temperature since it is assumed to be isentropic. The pressure ratio remains the same.

2. Heat Addition Process: The increase in maximum temperature results in a higher temperature at the end of the constant pressure heat addition process (Point 3). This increases the temperature difference between the hot and cold reservoirs, leading to a higher thermal efficiency.

3. Expansion Process: The expansion process is also not affected by the increase in maximum temperature since it is assumed to be isentropic. The pressure ratio remains the same.

4. Heat Rejection Process: The increase in maximum temperature does not affect the heat rejection process because the temperature difference between the hot and cold reservoirs remains the same.

Conclusion:

Increasing the maximum temperature of the air standard Brayton cycle while keeping the pressure ratio the same results in an increase in the air standard efficiency. This is because the increase in maximum temperature leads to a higher temperature difference between the hot and cold reservoirs, resulting in a higher thermal efficiency. Therefore, the correct answer is option 'C' - there is no change in the air standard efficiency.