A 33-year-old lady presents with polydipsia and polyuria. Her symptoms started soon after a road traffic accident 6 months ago. The blood pressure is 120/80 mm Hg with no postural drop. The daily urinary output is 6-8 litres. Investigation showed, Na 130 mEq/L, K.3.5 mEq/L, urea 15mgAIL, sugar-65 mg/dL. The plasma osmolality is 268 mosmoUL and urine osmolality 45 mosmol/L. The most likely diagnosis is -: (A) Central diabetes insipidus, (B) Nephrogenic diabetes insipidus, (C) Resolving acute tubular necrosis, (D) Psychogenic polydipsia
Answer is D. First lets go through the normal values of the indices required to solve this question​

Serum Sodium (Na) → 136-145 meq/L
Serum Potassium → 3.5-5.0 meq/L 
Serum Osmolality → 285-295 mmol/kg 
Serum Urea → 10-20 mg/dL 350
Urine Osmolality → 350 -1000 mosmol/kg.

Let's see the values in the patient

- Serum sodium        →     decreased
- Serum Osmolality   →   decreased
- Urine Osmolality     →  decreased