According to Wechsler, the definition of Intelligence includes -

The correct answer is Option (4) → Ability to think rationally and deal effectively with the environment

Wechsler, whose intelligence tests are most widely used, understood intelligence in terms of its functionality, i.e. its value for adaptation to environment. He defined it as the global and aggregate capacity of an individual to think rationally, act purposefully, and to deal effectively with her/his environment.