The weight of a person is given by W = m g, where m is the mass of the person and g is the effective acceleration due to gravity. The effective value of g varies with latitude on Earth primarily due to two factors: 1. Earth's Shape The Earth is not a perfect sphere; it is an oblate spheroid, flattened at the poles and bulging at the equator. This means the distance from the center of the Earth is greater at the equator than at the poles. According to the law of universal gravitation (G M / r²), gravitational force (and thus acceleration due to gravity) decreases with the square of the distance from the center. A larger distance at the equator results in a slightly weaker gravitational pull compared to the poles. 2. Earth's Rotation The Earth rotates on its axis, creating a centrifugal force acting outwards, perpendicular to the axis of rotation. This force reduces the effective downward gravitational force. This effect is maximum at the equator (where the linear velocity is highest and the force is directed directly opposite to gravity) and zero at the poles (where there is no linear motion around the axis).Both the increased distance from the center and the effect of centrifugal force due to rotation contribute to a lower effective 'g' at the equator compared to the poles, resulting in lower weight. Option B, stating the shape of the Earth, directly addresses the distance variation and is the primary shape-related reason.