Answer: B) the mouse population increases
A food chain is a linear series, in which food and energy is being transferred when one organism is fed or consumed by the other organism.
In the given, food chain, the grass is the producer, the mouse is the primary consumer as it feeds upon the grass, the snake is the secondary consumer as it feeds upon the mouse population, and lastly the hawk is the tertiary consumer as it feeds upon the snake. If the snake population is removed it will favor the growth of organisms belonging to lower trophic level. Mouse population being the lower trophic level after snake will increase in number.