the rattle snakes that fed on them would go hungry and die off. this would result in the eagles that fed off the snakes to go hungry and die as well.
There is no diagram in your question however if the kangaroo rats were killed off the organism that feeds on kangaroo rats or its direct consumer would suffer and may as well be killed because of lack of food supply. While the organisms that were eaten by kangaroo rats will increase its population because they have no eaters. When the food chain is disrupted, ecological imbalance may occur.
If an organism is removed from a food chain, the organism which feeds on it would suffer. Another example is the food chain ( leaf-caterpillar-bird-fox) If for instance the bird is taken out of the food chain, the foxes would starve because they would have no food to eat and would eventually die. The opposite thing happens to the caterpillar. Since they have nothing feed on them, they will increase in number and populate which will damage the leaf. The entire food chain was disrupted which can result to an ecological imbalance.
B The number of cactus plants would increase.