Zinc (Zn) is a moderately reactive metal that reacts with nitric acid (HNO3) to produce different products depending on the concentration of the acid.

a) N2O and NO2:
When zinc reacts with dilute nitric acid, it produces nitrogen dioxide (NO2) and nitrous oxide (N2O) as the main products.

b) NO2 and NO:
When zinc reacts with concentrated nitric acid, it produces nitrogen dioxide (NO2) and nitric oxide (NO) as the main products.

c) NO and N2O:
This combination of products is not observed when zinc reacts with either dilute or concentrated nitric acid.

Explanation:
1. Reaction with Dilute Nitric Acid:
When zinc reacts with dilute nitric acid, the following reaction occurs:

Zn + 4HNO3 → Zn(NO3)2 + 2H2O + N2O

In this reaction, the zinc displaces hydrogen from the nitric acid to form zinc nitrate (Zn(NO3)2) and water (H2O). Additionally, nitrogen dioxide (NO2) is formed as a byproduct, and nitrous oxide (N2O) is the main product. Nitrous oxide is a colorless gas with a slightly sweet odor.

2. Reaction with Concentrated Nitric Acid:
When zinc reacts with concentrated nitric acid, the following reaction occurs:

3Zn + 8HNO3 → 3Zn(NO3)2 + 2NO + 4H2O

In this reaction, three molecules of zinc react with eight molecules of nitric acid to form three molecules of zinc nitrate (Zn(NO3)2). Water (H2O) is also produced as a byproduct. In addition to these products, nitrogen dioxide (NO2) and nitric oxide (NO) are formed. Nitrogen dioxide is a reddish-brown gas with a pungent odor, while nitric oxide is a colorless gas with a sharp odor.

Conclusion:
The reaction of zinc with dilute nitric acid produces nitrous oxide (N2O) and nitrogen dioxide (NO2) as the main products. On the other hand, the reaction of zinc with concentrated nitric acid produces nitric oxide (NO) and nitrogen dioxide (NO2) as the main products.