Step 1: Understanding the Concept
Nitrogen is a diatomic gas, so \(C_p=\dfrac72R\).
Step 2: Key Formula or Approach
\(n=\dfrac{14}{28}=0.5\) mol and \(Q=nC_p\Delta T\).
Step 3: Detailed Explanation
\[ Q=0.5\times\frac72R\times48=0.5\times3.5\times48\,R=84R \]
Final Answer:
The heat needed is \(84R\), option (B).
\[ \boxed{84R\ \text{(B)}} \]