Microsomia" is defined as -
Bih weight below 90th percentile
Bih weight below 10th percentile
Bih weight below 20th percentile
Bih weight below 50th percentile
Ans. is 'b' i.e., Bih weight below 10' percentile Microsomia means small for date baby, i.e. newborn baby with a bih weight less than 10th percentile.