The correct answer is option 3, which states that a special category state invariably has a low literacy rate.

Option 1 suggests that a special category state is a border state. This means that it is located on the border of a country or another region. While this may or may not be true for all special category states, it is a possibility in some cases.

Option 2 states that a special category state has harsh terrain. This means that the geographical features of the state are challenging, such as rugged mountains, dense forests, or arid deserts. Again, while not necessarily true for all special category states, it is possible in some cases.

Option 3, the correct answer, claims that a special category state invariably has a low literacy rate. However, this statement is not accurate. A special category state can have varying levels of literacy, just like any other state. The literacy rate depends on various factors such as government policies, access to education, and socio-economic conditions.

Option 4 suggests that a special category state has poor infrastructure. This can include inadequate roads, transportation, schools, hospitals, and other essential facilities. While this may be true in some cases, it is not a characteristic that is universally applicable to all special category states