Step 1: Understanding the Concept:
For diatomic gas, \(C_p = \frac{7}{2}R\), \(C_v = \frac{5}{2}R\). At constant pressure, \(Q = nC_p\Delta T\). \(\Delta U = nC_v\Delta T\).
Step 2: Detailed Explanation:
Fraction = \(\frac{\Delta U}{Q} = \frac{nC_v\Delta T}{nC_p\Delta T} = \frac{C_v}{C_p} = \frac{\frac{5}{2}R}{\frac{7}{2}R} = \frac{5}{7}\).
Step 3: Final Answer:
Thus, fraction = \(5/7\).