Answer:
Volume of 22 drop will be 0.68 ml
Step-by-step explanation:
We have given volume of one drop = 0.031 ml 
We know that 1 liter = 1000 ml 
So 

So 0.031 ml will be equal to 

We have to find the volume of 22 drop 
For finding volume of 22 drop we have to multiply volume of one drop by 22
So volume of 22 drop will be 

So volume of 22 drop will be 0.68 ml