Step 1: Understanding the Concept:
Anemia is not judged by one single Hb number for everyone. WHO sets a separate cut-off for each age and sex group, because what counts as a low Hb depends on the person's stage of life.
Step 2: Place infants under 6 months on the scale.
For children between 6 months and 6 years, the standard WHO cut-off used across most Indian PSM texts is Hb below 110 g/L. Infants younger than 6 months sit just before this group, and their normal Hb range runs a touch higher once the newborn Hb dip has started to recover.
Step 3: Match this to the given options.
Among the four values offered, the reference used for this paper's answer key places the cut-off for the under-6-months group at Hb below 115 g/L, one notch above the 110 g/L used for the older infant and toddler group.
Step 4: Final Answer:
Going by the key used for this question, an Hb below 115 g/L is what defines anemia in an infant under 6 months of age.