Illusion is -

Ans is 'b' i.e. Alteration of perception of one's reality o Altered perception of real object - Illusiono False perception without external stimulus - Hallucination.Illusiono Illusions are altered perception in which a real external object is combined with imagery to produce false internal percept. In simple words, illusion is misinterpretation of an actual sensory input. For example:-i) Hearing once name in a train whistle:- Train whistle is a real external stimulus, which is perceived as once name (false internal percept).ii) Mistaking a stick or rope for snake in dark room:- Stick is a real external object, which is perceived falsely as snake.In illusion:-i) Sensory input is in external atmosphere.ii) Percept is in internal atmosphere (inner subjective space, i.e., inside the mind).o Illusions are most commonly seen in delirium.