Newton’s first law of motion is also called Galileo’s law of:
A. Conservation of momentum
B. Inertia
C. Friction
D. Conservation of mass

Hint: Consider a body at rest and another body in motion with constant velocity. Compared with the situation where in one situation we apply an external force and in the other condition we don’t have any external force on them. Define their state. We will get Newton's first law from the second condition.

Complete step-by-step answer:
Newton’s first law of motion can be defined as if the net external force on a body is zero, its acceleration will be zero. If there is an external force applied, then only we can get an acceleration.
We can simply state the above law as every body which is in a state of rest will continue to be in the state of rest or every body which is in motion in a straight line will continue to be in this state of motion unless we apply any external force on it.
Galileo gave the concept of motion as the state of rest and the state of uniform linear motion are equivalent. According to him, if the net external force on an object is zero, an object's rest continues to be at rest and a body in motion continues to move with uniform velocity. This property of the body is called the inertia. A body does not change its state of rest or state of motion unless we apply an external force on it. This is Galileo's law of inertia.
So, we can say that Newton’s first law of motion is also called the Galileo’s law of inertia.
The correct option is (B).

Note: Newton’s laws are built on Galileo’s laws and Galileo’s law of inertia was the starting point of Newton's first law of motion.
We always experience many forces like gravitational force, frictional force etc acting on a body. But then also we get a state of rest or state of uniform motion on earth because all the forces acting on a body cancels out to give zero total external force.