Explanation:

- Let’s break it down: inertia is all about how much an object resists a change in its motion. The more inertia, the harder it is to get moving—or to stop.

- Velocity (Option 1) is just how fast and in what direction something’s going. It doesn’t tell us how stubborn an object is about starting or stopping.

- Acceleration (Option 2) is how quickly velocity changes. Again, not a measure of how much something resists moving.

- Mass (Option 3) is the key. It’s literally the measure of inertia. Heavier objects have more inertia; lighter ones have less.

- Weight (Option 4) is mass influenced by gravity; it depends on where you are (Earth, Moon, wherever). But inertia is pure mass, gravity or not.

- So, the short version: mass is what really gauges inertia. The other options don’t fit the bill.