Concept: This question tests your understanding of the components of a reflex arc and the sequential pathway of an action potential during a reflex action.

Why (B) is correct: A reflex arc is the neural pathway that mediates a reflex action. When a stimulus is applied, it is first detected by a sensory receptor (V). This receptor generates an action potential, which is then transmitted by a sensory neuron (IV) (afferent neuron) towards the Central Nervous System (CNS). In the CNS (often in the spinal cord), the sensory neuron synapses with an interneuron (II) (relay neuron). The interneuron then transmits the signal to a motor neuron (III) (efferent neuron), which carries the action potential away from the CNS to the effector organ (I) (e.g., muscle or gland) to produce a response. Therefore, the correct order is V → IV → II → III → I.

Why other options are wrong:

A) This order incorrectly places the motor neuron before the interneuron.

C) This order incorrectly places the motor neuron before the sensory neuron and the interneuron at the end.

D) This order incorrectly places the interneuron before the sensory neuron and the motor neuron before the effector organ.

Common Mistake: Students often confuse the order of sensory and motor neurons, or forget the role of the interneuron in polysynaptic reflexes.

NEET Tip / Mnemonic: Remember the flow as Stimulus → Receptor → Afferent (Sensory) → Interneuron → Efferent (Motor) → Effector → Response. A simple mnemonic for the pathway is SRAIER.

Correct Answer: (B)