As per WHO low bih weight is defined as -

According to WHO , low bih weight is defined as bih weight of less than 2.5 kg. Hence option 1 is the most appropriate answer. Coming to other options, Option 2- bih weight less than 10th percentile for gestational age is known as small for date babies Option3and 4, Extremely preterm is less than 28 wks Very preterm is 28-32 weeks Moderate to late preterm is 32 to 37 weeks Reference Park&;s textbook of preventive and social medicine 23rd edition pg 536