The minimum number of links in a single degree-of-freedom planar mechanism with both higher and lower kinematic pairs is 2.

Explanation:
A planar mechanism is a mechanical system that operates in a two-dimensional plane. It consists of a series of links connected by joints, and the motion of the mechanism is determined by the type of joints used.

A higher kinematic pair is a type of joint where the relative motion between the two connected links is constrained by contact between their surfaces. Examples of higher kinematic pairs include rolling, sliding, and screw pairs.

A lower kinematic pair is a type of joint where the relative motion between the two connected links is constrained by a point or a line contact. Examples of lower kinematic pairs include revolute, prismatic, and cylindrical pairs.

In order to have both higher and lower kinematic pairs in a planar mechanism, we need at least two links connected by two different types of joints. Let's consider the following scenario:

1. Link 1: This is the fixed link of the mechanism. It provides a reference frame for the motion of the other links.

2. Link 2: This link is connected to Link 1 by a revolute joint, which is a lower kinematic pair. The revolute joint allows Link 2 to rotate about a fixed axis relative to Link 1.

3. Link 3: This link is connected to Link 2 by a sliding joint, which is a higher kinematic pair. The sliding joint allows Link 3 to translate along a fixed direction relative to Link 2.

In this mechanism, Link 1 is fixed, Link 2 can rotate about a fixed axis, and Link 3 can translate along a fixed direction. The relative motion between the links is constrained by the combination of the revolute and sliding joints.

Therefore, the minimum number of links in a single degree-of-freedom planar mechanism with both higher and lower kinematic pairs is 2.