Weight and the force of gravity:
Weight is the force experienced by an object due to the gravitational pull of the Earth. It is measured in Newtons (N). The weight of an object can be calculated using the formula W = mg, where W is the weight, m is the mass of the object, and g is the acceleration due to gravity (approximately 9.8 m/s² on Earth).

Effect of altitude on weight:
When an object is taken to a higher altitude, away from the surface of the Earth, the force of gravity acting on it decreases slightly. This is because the gravitational pull decreases with increasing distance from the center of the Earth. As a result, the weight of the object also decreases.

Spring balance and weight measurement:
A spring balance is an instrument used to measure the weight of an object. It works based on Hooke's law, which states that the force exerted by a spring is directly proportional to the displacement of its end. The spring balance consists of a spring attached to a hook, and the object whose weight is to be measured is hung from the hook. The reading on the spring balance indicates the weight of the object.

Effect of altitude on spring balance reading:
As the aeroplane goes up in altitude, the distance between the object and the center of the Earth increases, resulting in a decrease in the force of gravity acting on the object. However, the spring balance still measures the force exerted by the object, which is its weight.

Explanation of the answer (option D):
Initially, when the aeroplane starts ascending, the distance between the object and the center of the Earth increases, causing a decrease in the force of gravity acting on the object. However, the spring balance still measures the weight of the object, which is the force exerted by it. Therefore, initially, the reading on the spring balance will increase.

As the aeroplane continues to ascend further, the distance between the object and the center of the Earth keeps increasing, resulting in a further decrease in the force of gravity. Eventually, a point will be reached where the decrease in the force of gravity outweighs the increase in the distance, causing the reading on the spring balance to start decreasing.

Therefore, the correct answer is option D - the reading on the spring balance will first increase and then decrease as the person with the spring balance and the hanging body goes up in the aeroplane.