Answer:
0.25 moles of N₂
Step-by-step explanation:
The number of moles of NH₃ produced is 0.50. 
 The given reaction is shown below 
 
N ₂ ( g ) + 3 H ₂ ( g ) → 2 N H ₃ (g ) 
 It is clear from the reaction that; 
 2 moles of N H ₃ are produced when 1 mole of N₂ react. 
 Therefore, 1 mole of N H ₃ is produced when 0.5 mole N ₂
 Thus, 0.5 moles of N H ₃ are produced when 0.5 × 0.5 moles of N ₂ react. 
 Hence, 0.5 moles of N H ₃are produced when 0.25 moles of N ₂ react. 
 Therefore, the number of moles of N₂ reacted to form 0.5 moles of N H ₃ is 0.25