Answer:
The gizzard
Step-by-step explanation:
The organ inside the chicken that stores sand would be the gizzard.
The gizzard of chickens represents an important part of the digestive system of the animal. Food particles are ground into finer, more easily digestible forms within the gizzard before being passed into the small intestine for further processing. The gizzard is able to perform the grinding through the use of grits - small particles of sand/pebbles.
Hence, the correct answer to the organ that stores sand inside the chicken is the gizzard.