a)
Buoyant force varies directly with the density, volume and mass of the displaced fluid. According to Archimedies principle, the buoyant force equals the weight of fluid displaced. The lead sphere has more weight than the aluminium sphere. This means that it would displace more fluid. Thus, the lead sphere experiences a greater buoyant force
b) The buoyant force is is also affected by the type of fluid. Different fluids have different densities. If the density of the object is greater than the density of the fluid, it tends to sink. Thus, the answer is Yes