The question asks about the land surface with the highest albedo. Albedo refers to the measure of how much of the incident light or radiation is reflected by a surface. Higher albedo means more light or radiation is reflected, while lower albedo means more light or radiation is absorbed.

Option 1: A snow-covered mountain. In general, snow has a high albedo because it is highly reflective. Sunlight tends to be reflected off the white surface of the snow, resulting in a high albedo.

Option 2: A barren rocky piedmont surface. Rocks are generally not reflective, and they absorb sunlight. Therefore, a rocky surface would have a lower albedo compared to snow.

Option 3: A sandy desert. Sandy deserts have a moderate albedo. Although sand can reflect some sunlight, it also absorbs some sunlight, resulting in a relatively lower albedo compared to snow.

Option 4: A mangrove forest. Mangrove forests have a low albedo because they have dense vegetation that absorbs sunlight. This absorption of light results in a lower reflection and therefore a lower albedo.

Based on the explanations, option 1, a snow-covered mountain, has the highest albedo compared to the other options provided.