To determine which block, aluminum or iron, experiences a greater buoyant force, we need to consider the concept of buoyant force and the factors that affect it. Buoyant force is an upward force exerted by a fluid that counteracts the weight of an object submerged in it. According to Archimedes' principle, the magnitude of the buoyant force is equal to the weight of the fluid displaced by the submerged object.

Now, let's compare aluminum and iron blocks in terms of buoyant force:

1. Density:

- Aluminum has a lower density compared to iron. The density of aluminum is approximately 2.7 g/cm³, while the density of iron is around 7.8 g/cm³.

2. Volume of Fluid Displaced:

- Since the buoyant force is directly proportional to the volume of fluid displaced, a block with a larger volume submerged in the fluid will experience a greater buoyant force.

Considering these factors, the aluminum block, despite having a smaller mass compared to the iron block, will displace a larger volume of fluid due to its lower density. Consequently, the aluminum block will experience a greater buoyant force compared to the iron block.

Therefore, the aluminum block experiences a greater buoyant force.