Question

Why is Weight not constant at all d places

Answer 1

The weight, w of any object on Earth is measured as w = mg
where m is the mass of the object and g is the acceleration due to gravity of earth.
The value of g is not constant at all the places and is calculated as $g=\frac{\mathrm{G}M}{R^2}$
where G is gravitational constant, M is mass of earth, which is also constant
R is the radius of Earth, which varies as the earth is not perfectly spherical.
Thus weight also varies as the value of g varies.