How do i give the number of significant figures in 0.0037 mm

According to coulomb's law, how would the electrical force between particles change if the product of their electrical charge increased?

Suppose a lab group reports a ppercent yield of sand of 105. is it really possible to collect more sand than was originally represented? what is the possible explanation for the extra product?

How can a give a full method for the experiment of separating sand from water by filtration? 1-materials 2-steps 3-conclusion also for water and salt separated by the evaporation or distillation process