Will a marble and marshmallow have same buoyancy?

No, a marble and marshmallow will not have the same buoyancy. Buoyancy is the upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. The buoyant force is equal to the weight of the fluid displaced by the object.

The density of an object is defined as its mass per unit volume. The more dense an object is, the more matter it has packed into a given volume. The density of a marble is much greater than the density of a marshmallow. This means that a marble will displace less water than a marshmallow of the same size.

The buoyant force acting on an object is equal to the weight of the water displaced by the object. Since a marble displaces less water than a marshmallow, the buoyant force acting on a marble will be smaller than the buoyant force acting on a marshmallow. This means that a marble will sink in water, while a marshmallow will float.