If deer is missing from the food chain, the correct answer is (d) The population of tiger decreases and the population of grass increases.
Explanation:
Tiger population decrease:
Since tigers prey on deer, the absence of deer will lead to a lack of food for tigers, causing their population to decline.
Grass population increase:
With no deer to consume the grass, the plant population will grow unchecked, resulting in an increase in grass.
Why other options are incorrect:
(a) The population of tiger increases:
This is the opposite of what happens. Tigers require deer as their prey, so their population will decrease without deer.
(b) The population of grass decreases:
The opposite occurs; the grass population will increase due to a lack of herbivores to eat it.
(c) Tiger will start eating grass:
Tigers are predators that typically consume meat. While they might attempt to eat other food sources in the absence of deer, switching to herbivory is not a natural adaptation for most tiger species.