Completely soluble means when we pour some substances into the water, they completely disappear in water. We cannot see their particles.

In the given options, glucose is completely soluble in water.

i. The particles of glucose are so small; hence it becomes soluble in water.

ii. On the other hand, chalk powder, tea leaves and saw dust are insoluble in water.

iii. We can see their particles in water which settles down at the bottom.