The correct option is C The relationship is non-linear.
Let the cost of a balloon is represented as C unit and number of balloons purchased be n.
Here, n is the independent variable.
Cost of a balloon is inversely proportional to number of balloons purchased.
⇒C∝1n
⇒C=k1n
where k is a constant of proportionality.
⇒C=kn−1
The exponent of the independent variable is −1.
Hence, this is a non-linear function.