1. Balancing the Reaction:
To balance the given reaction in an acidic medium:
\[
\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6\text{Fe}^{2+} \rightarrow 2\text{Cr}^{3+} + 6\text{Fe}^{3+} + 7\text{H}_2\text{O}.
\]
2. Identify \(X\), \(Y\), and \(Z\):
- \(X = 14\) (moles of H\(^+\)),
- \(Y = 2\) (moles of Cr\(^3+\)),
- \(Z = 7\) (moles of H\(_2\)O).
3. Sum of \(X + Y + Z\):
\[
X + Y + Z = 14 + 2 + 7 = 23.
\]
Final Answer: \( \boxed{23} \).