Step 1: Neonatal mortality rate (NMR) is the number of deaths under 28 days of age per 1000 live births, a sensitive marker of perinatal and newborn care quality.
Step 2: Across India the lowest NMR is recorded in Kerala. Kerala is not in the option list, so we choose the best among those given.
Step 3: Among Delhi, Tamil Nadu, Karnataka and Maharashtra, Tamil Nadu has the lowest neonatal mortality, reflecting its strong maternal and child health services. This makes option b correct.
Step 4: The remaining states, though performing well, report higher NMR than Tamil Nadu, so they are not the answer.