Q. Illustrate is negative mass antimatter?

Answer:-

It is false there is really no such thing as negative mass. Yet antimatter has mass which is always a positive (that is, greater-than-zero) quantity.

There is nevertheless the concept of effective mass or apparent mass which can be negative. When an thing is submerged in water its apparent weight is reduced by an amount equivalent to the weight of water it displaces. For instance if a 10-pound rock is dropped into a bucket of water and displaces one pound of water the effectual weight of the rock under water is nine pounds.

However what if you submerge something a lot less dense than a rock let's says a big ball of Styrofoam in its place. Not as ecological but less violent. In that situation the weight of the water displaced by the ball will be far greater than the actual weight of the ball thus when you subtract the weight of the water from the weight of the ball you'll get a negative number. In other sense the effectual weight of the ball under water will be negative and the ball will tend to rise. It will struggle your efforts to submerge it greatly as big ball would if you submerged his head but for reasons other than mere buoyancy.