Place the following parts of a reflex arc in the correct order beginning with the sensory receptor. (1) Motor neuron (2) Interneuron (3) Effector (4) Sensory neuron (5) Sensory receptor

Reflex arc can be defined as the pathway taken by an impulse which helps out body to react in response to any specific demand by the environment.
A Reflex Action can be defined as the immediate response of the body to a sudden environmental stimulus.
Impulses in the body are carried by means of neurons. As a reflex action demands an immediate response, so the response to these impulses are generated in the spinal cord and the impulses are not send to the brain (to save time).
The pathway taken by an impulse is explained below:

The Receptor organ recognises the stimulus.
It sends the message as an impulse to the Sensory neuron.
The Sensory neuron carries the message of the impulse to the Spinal cord.
In the Spinal cord, there are Inter-neurons that take up the message, decides the action to be taken and sends the response to the Motor neuron.
The Motor neuron conducts the response message from the inter-neuron to the Effector organ.
The Effector organ gives the appropriate response.