The equation of demand curve of a good for a consumer is given to be $pq = e$ where e is a constant. What will be the shape of the demand curve?

Downward sloping rectangular hyperbola.

The correct answer is Option (3) → Downward sloping rectangular hyperbola.

Given equation: p×q=e i.e. p =e/q ( e is constant)

As quantity q increases, price p decreases in such a way that their product remains constant.

It is a rectangular hyperbola because the area under the curve (which represents total expenditure, $p\times q$) is constant at all points on the curve. This means the Price Elasticity of Demand is unity (${\text{E}}^d=1$) throughout the curve.