Which of the following variables is measured on the ordinal scale-
When data is ranked e.g. mild, moderate, severe  → ordinal scale is used. Therefore the severity of anemia is measured on the ordinal scale.
Type of anemia can be divided into qualitative categories (Macrocytic/microcytic, hemolytic/non-hemolytic) → Nominal scale is used.
Serum ferritin and hemoglobin are quantitative variables with a possible absolute zero value → Ratio scale is used.
Type of anemia
Severity of anemia
Hemoglobin
Serum ferritin