What happens when Concentrated HNO3 is dropped onto hot charcoal?

What happens when Concentrated HNO3 is dropped onto hot charcoal?

Answer: When concentrated HNO3 is dropped (drop by drop) on hot charcoal (carbon), carbon oxidizes to CO2 gas and HNO3 reduces to nitrogen dioxide (NO2).

C + 4HNO3 = CO2 ↑ + 4NO2 ↑ + 2H2O