The correct answer is C) change the direction of steam flow. In an impulse turbine, the fixed blades, also known as nozzle blades or guide vanes, function to change the direction of the steam flow. As the steam passes through the fixed blades, the blades redirect the steam at an angle, causing it to change direction before it reaches the rotating blades. This change in steam flow direction is crucial for the efficient operation of the turbine, as it allows the steam to impart its maximum amount of energy to the rotating blades, ultimately driving the turbine. The other options are incorrect because they do not accurately describe the primary function of the fixed blades in an impulse turbine. Option A) decrease steam velocity is incorrect, as the fixed blades are designed to accelerate the steam flow. Option B) equalize pressure differences is also incorrect, as the fixed blades are not primarily responsible for equalizing pressure differences within the turbine. Option D) prevent steam turbulence is partially correct, but it does not capture the full purpose of the fixed blades, which is to change the direction of steam flow.