Leaf is modified into thorn where water availability is lowgive reason?

To help conserve water or prevent loss via transpiration from the leaves

Explanation:

Some plants are found growing in habitats with little or no moisture content as annual rainfall is very low. These plants are called xerophytic plants. However, despite the low water condition, these plants are adapted to the environment and still survive.

One of their adaptation (structural) is that their leaves are reduced to thorns. Ideally, plants tend to lose water via the stomata on the leaves in a process called TRANSPIRATION. Hence, the leaves of plants adapted to a xerophytic habitat is modified to thorns in order to prevent water loss from the leaves and conserve the water.