Explanation:

An irrigation outlet is said to be proportional when its flexibility is equal to 1. This means that the outlet is able to adjust its flow rate in proportion to changes in pressure or head.

Flexibility:

Flexibility refers to the ability of an irrigation outlet to respond to changes in pressure or head by adjusting its flow rate. When an outlet has a flexibility of 1, it means that it is able to maintain a constant flow rate regardless of changes in pressure or head.

Proportional Outlet:

A proportional irrigation outlet is designed to provide a constant flow rate, regardless of changes in pressure or head. This is important in irrigation systems because it ensures that each section of the field receives an equal amount of water, regardless of variations in pressure.

Benefits of Proportional Outlets:

1. Uniform Water Distribution: Proportional outlets ensure that each section of the field receives the same amount of water, resulting in uniform water distribution. This is important for crop growth and yield.

2. Efficient Water Use: By providing a constant flow rate, proportional outlets help to improve the efficiency of water use in irrigation systems. This reduces wastage and promotes sustainable water management.

3. Improved Crop Performance: Proportional outlets ensure that crops receive a consistent water supply, which is essential for their growth and performance. This can lead to improved crop yields and quality.

4. Reduced Water Stress: Proportional outlets help to minimize water stress on crops by providing a steady water supply. This is particularly important during periods of high water demand or drought.

5. Easy System Design: Proportional outlets simplify system design by eliminating the need for complex pressure regulation devices. This reduces the cost and complexity of irrigation systems.

Conclusion:

In conclusion, a proportional irrigation outlet is one that maintains a constant flow rate regardless of changes in pressure or head. This ensures uniform water distribution, efficient water use, improved crop performance, reduced water stress, and simplified system design. Therefore, the correct answer to the given question is option 'B' (flexibility = 1).