Which abbreviation signifies 'Grains' in the context of weight?

The abbreviation that signifies 'Grains' in the context of weight is "gr." This abbreviation comes from the Latin word "granum," meaning grain. In medical and pharmaceutical contexts, grains are a traditional unit of measure, particularly used for dosing medications where precise, small amounts are necessary.

The other abbreviations provided serve different purposes: "g" stands for grams, which is a metric unit of mass; "mcg" represents micrograms, a measure used for extremely small quantities; and "ML" refers to milliliters, a unit of volume. Understanding these distinctions is crucial for accurate dosing and measurements in medical settings.