(1) 1, 2,3 The volume of immersed liquid increases, the indicated value of spring dynamometer decreases, and the buoyancy gradually increases; When submerged, the reading of the spring dynamometer does not change, and the buoyancy does not change.

So the answer is: the larger the volume of immersion liquid, the greater the buoyancy; ? When diving into the water, the depth changes, while the buoyancy of the object remains unchanged.

(2) The larger the volume of1,2,3 immersed in liquid, the greater the buoyancy.

So the answer is: (4).

(3) Add salt into the water and stir slowly. With the increase of salt water density, the eggs gradually floated up and finally floated up.

So the answer is:

(1) Put the eggs in clear water and the eggs will sink to the bottom. At this point, the buoyancy of the egg is less than gravity.

(2) add salt to the beaker and change the density of the liquid until the egg floats to the surface. Buoyancy equals the gravity of an egg.

Conclusion: With the increase of liquid density, the buoyancy of objects increases.