**Category:** Inorganic Chemistry  
**Subtype:** Chemical Reactions  
**Problem Description:** Identify the gas produced when copper (Cu) reacts with concentrated hot nitric acid (\(\mathrm{HNO}_{3}\)). The gas is described as having a reddish-brown color.  

**Options for the gas (X):**  
A. \(\mathrm{N}_{2}\)  
B. \(\mathrm{NO}_{2}\)  
C. NO  
D. \(\mathrm{N}_{2} \mathrm{O}\)