The pyramid of the biomass depicts the depicts the bio productivity at each level of the organism. The producers are the organism, which have the highest number of the productivity and their number is comparatively higher than the consumers.
In the pyramid of biomass, the herbivore comes after the producers and then the carnivores. In this case, the grass would have highest productivity, so, it would occupy lower most position, then mouse and then snake.
So, the order in a biomass pyramid from lowest to highest is grass, mouse, snake.