In the expression 1:100,000, what does it signify?

The expression 1:100,000 signifies a dilution ratio, indicating that there is one part of a substance in a total volume of 100,000 parts of solution. In the context of the given options, the correct interpretation would mean that for every 1 unit of the substance, there is a vast volume of 100,000 units of the solvent.

When considering this ratio, 1 gram in 100,000 cc's of solution provides a clear understanding of the concentration. Here, 1 gram represents the quantity of the active substance, while 100,000 cc (cubic centimeters) refers to the total volume of the solution in which the substance is diluted.

This explains the concept of dilution in pharmacology and other areas, where a small amount of a substance is mixed with a significantly larger volume to create a manageable concentration for various applications, such as medications or chemical solutions.